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Add anagram exercise (#266)
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‎config.json

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"prerequisites": [],
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"difficulty": 4
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},
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{
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"slug": "anagram",
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"name": "Anagram",
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"uuid": "4172a5bb-0c8e-4a66-9551-8b46acdfc57a",
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"practices": [],
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"prerequisites": [],
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"difficulty": 5
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},
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{
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"slug": "diamond",
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"name": "Diamond",

‎exercises/practice/anagram/.docs/hints.md

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# Hints
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## General
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- The `$t0-9` registers can be used to temporarily store values
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- The instructions specify which registers are used as input and output

‎exercises/practice/anagram/.docs/instructions.append.md

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# Instructions append
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## Input/Output format
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Each set of words is represented as a null-terminated string, with a newline character at the end of each word.
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An example would be `"tones\nnotes\nSeton\n"`
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## Registers
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| Register | Usage | Type | Description |
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| -------- | ------------ | ------- | -------------------------------------------------------------- |
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| `$a0` | input | address | null-terminated target string, without newline |
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| `$a1` | input | address | null-terminated candidates string with newline after each word |
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| `$a2` | input/output | address | null-terminated output string with newline after each word |
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| `$t0-9` | temporary | any | for temporary storage |

‎exercises/practice/anagram/.docs/instructions.md

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# Instructions
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Your task is to, given a target word and a set of candidate words, to find the subset of the candidates that are anagrams of the target.
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An anagram is a rearrangement of letters to form a new word: for example `"owns"` is an anagram of `"snow"`.
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A word is _not_ its own anagram: for example, `"stop"` is not an anagram of `"stop"`.
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The target and candidates are words of one or more ASCII alphabetic characters (`A`-`Z` and `a`-`z`).
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Lowercase and uppercase characters are equivalent: for example, `"PoTS"` is an anagram of `"sTOp"`, but `StoP` is not an anagram of `sTOp`.
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The anagram set is the subset of the candidate set that are anagrams of the target (in any order).
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Words in the anagram set should have the same letter case as in the candidate set.
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Given the target `"stone"` and candidates `"stone"`, `"tones"`, `"banana"`, `"tons"`, `"notes"`, `"Seton"`, the anagram set is `"tones"`, `"notes"`, `"Seton"`.

‎exercises/practice/anagram/.docs/introduction.md

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# Introduction
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At a garage sale, you find a lovely vintage typewriter at a bargain price!
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Excitedly, you rush home, insert a sheet of paper, and start typing away.
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However, your excitement wanes when you examine the output: all words are garbled!
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For example, it prints "stop" instead of "post" and "least" instead of "stale."
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Carefully, you try again, but now it prints "spot" and "slate."
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After some experimentation, you find there is a random delay before each letter is printed, which messes up the order.
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You now understand why they sold it for so little money!
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You realize this quirk allows you to generate anagrams, which are words formed by rearranging the letters of another word.
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Pleased with your finding, you spend the rest of the day generating hundreds of anagrams.

‎exercises/practice/anagram/.meta/config.json

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{
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"authors": [
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"keiravillekode"
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],
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"files": {
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"solution": [
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"impl.mips"
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],
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"test": [
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"runner.mips"
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],
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"example": [
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".meta/example.mips"
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]
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},
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"blurb": "Given a word and a list of possible anagrams, select the correct sublist.",
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"source": "Inspired by the Extreme Startup game",
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"source_url": "https://github.com/rchatley/extreme_startup"
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}

‎exercises/practice/anagram/.meta/example.mips

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# | Register | Usage | Type | Description |
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# | -------- | ------------ | ------- | -------------------------------------------------------------- |
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# | `$a0` | input | address | null-terminated target string, without newline |
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# | `$a1` | input | address | null-terminated candidates string with newline after each word |
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# | `$a2` | input/output | address | null-terminated output string with newline after each word |
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# | `$sp` | stack | address | stack pointer, points to target letter count table |
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# | `$a3` | temporary | address | points to candidate letter count table |
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# | `$v0` | temporary | address | points to newline or null at end of word |
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.macro count_letters (%word, %table)
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# %word is address of input word
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# %table is address of letter count table to populate
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# $v0 is set to adddress of word terminator (\n or \0)
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move $v0, %word
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addiu $t1, %table, 104
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clear:
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subiu $t1, $t1, 4
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sw $zero, 0($t1)
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bne $t1, %table, clear
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b read
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count:
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addiu $v0, $v0, 1 # address of next letter in input word
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or $t0, $t0, 32 # force to lower case
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subiu $t0, $t0, 'a'
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sltiu $t1, $t0, 26 # $t1 is set to 1 if $t0 is alphabetic, otherwise 0
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beqz $t1, read # jump to next character if not alphabetic
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sll $t0, $t0, 2
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add $t1, %table, $t0 # address for letter count
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lw $t2, 0($t1)
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addi $t2, $t2, 1 # increment letter count
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sw $t2, 0($t1)
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read:
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lb $t0, 0($v0)
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bge $t0, 32, count # repeat until end of word
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.end_macro
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.globl find_anagrams
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find_anagrams:
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subiu $sp, $sp, 208 # Allocate stack space for letter count tables
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addiu $a3, $sp, 104 # Address of candidate letter count table
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count_letters ($a0, $sp) # Populate target letter count table
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j consider_candidate
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copy_next_letter:
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addiu $a1, $a1, 1
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copy_word:
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# Copy word $a1..$v0 inclusive to $a2
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lb $t0, 0($a1)
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sb $t0, 0($a2)
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addiu $a2, $a2, 1
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bne $a1, $v0, copy_next_letter
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next_candidate:
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addiu $a1, $v0, 1
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lb $t0, 0($a1)
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bnez $t0, consider_candidate
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sb $zero, 0($a2) # Write null terminator
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addiu $sp, $sp, 208 # Restore original stack pointer
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jr $ra
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consider_candidate:
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count_letters ($a1, $a3)
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move $t5, $sp # Pointer into target letter count table
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move $t6, $a3 # Pointer into candidate letter count table
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compare_count:
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lw $t7, 0($t5)
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lw $t8, 0($t6)
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addiu $t5, $t5, 4 # Increment pointers
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addiu $t6, $t6, 4
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bne $t7, $t8, next_candidate # Reject candidate if count does not match
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bne $t5, $a3, compare_count # Repeat until all 26 counts have been compared
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# The letter counts match.
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# We now perform a case-insentitive string comparison
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move $t5, $a0 # Pointer into target string
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move $t6, $a1 # Pointer into candidate string
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compare_character:
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lb $t7, 0($t5)
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lb $t8, 0($t6)
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addiu $t5, $t5, 1 # Increment pointers
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addiu $t6, $t6, 1
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# Force each letter to lowercase
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blt $t7, 'A', target_letter_ready
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bgt $t7, 'Z', target_letter_ready
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addi $t7, $t7, 32
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target_letter_ready:
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blt $t8, 'A', candidate_letter_ready
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bgt $t8, 'Z', candidate_letter_ready
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addi $t8, $t8, 32
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candidate_letter_ready:
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bne $t7, $t8, copy_word # Candidate word is not the same as target word
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bne $t6, $v0, compare_character # Repeat until the whole word has been compared
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b next_candidate # Skip candidate word, because it is the target word

‎exercises/practice/anagram/.meta/tests.toml

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[dd40c4d2-3c8b-44e5-992a-f42b393ec373]
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description = "no matches"
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[b3cca662-f50a-489e-ae10-ab8290a09bdc]
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description = "detects two anagrams"
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include = false
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[03eb9bbe-8906-4ea0-84fa-ffe711b52c8b]
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description = "detects two anagrams"
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reimplements = "b3cca662-f50a-489e-ae10-ab8290a09bdc"
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[a27558ee-9ba0-4552-96b1-ecf665b06556]
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description = "does not detect anagram subsets"
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[64cd4584-fc15-4781-b633-3d814c4941a4]
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description = "detects anagram"
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[99c91beb-838f-4ccd-b123-935139917283]
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description = "detects three anagrams"
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[78487770-e258-4e1f-a646-8ece10950d90]
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description = "detects multiple anagrams with different case"
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[1d0ab8aa-362f-49b7-9902-3d0c668d557b]
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description = "does not detect non-anagrams with identical checksum"
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[9e632c0b-c0b1-4804-8cc1-e295dea6d8a8]
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description = "detects anagrams case-insensitively"
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[b248e49f-0905-48d2-9c8d-bd02d8c3e392]
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description = "detects anagrams using case-insensitive subject"
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[f367325c-78ec-411c-be76-e79047f4bd54]
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description = "detects anagrams using case-insensitive possible matches"
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[7cc195ad-e3c7-44ee-9fd2-d3c344806a2c]
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description = "does not detect an anagram if the original word is repeated"
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include = false
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[630abb71-a94e-4715-8395-179ec1df9f91]
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description = "does not detect an anagram if the original word is repeated"
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reimplements = "7cc195ad-e3c7-44ee-9fd2-d3c344806a2c"
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[9878a1c9-d6ea-4235-ae51-3ea2befd6842]
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description = "anagrams must use all letters exactly once"
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[85757361-4535-45fd-ac0e-3810d40debc1]
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description = "words are not anagrams of themselves (case-insensitive)"
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include = false
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[68934ed0-010b-4ef9-857a-20c9012d1ebf]
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description = "words are not anagrams of themselves"
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reimplements = "85757361-4535-45fd-ac0e-3810d40debc1"
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[589384f3-4c8a-4e7d-9edc-51c3e5f0c90e]
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description = "words are not anagrams of themselves even if letter case is partially different"
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reimplements = "85757361-4535-45fd-ac0e-3810d40debc1"
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[ba53e423-7e02-41ee-9ae2-71f91e6d18e6]
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description = "words are not anagrams of themselves even if letter case is completely different"
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reimplements = "85757361-4535-45fd-ac0e-3810d40debc1"
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[a0705568-628c-4b55-9798-82e4acde51ca]
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description = "words other than themselves can be anagrams"
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include = false
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[33d3f67e-fbb9-49d3-a90e-0beb00861da7]
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description = "words other than themselves can be anagrams"
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reimplements = "a0705568-628c-4b55-9798-82e4acde51ca"
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[a6854f66-eec1-4afd-a137-62ef2870c051]
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description = "handles case of greek letters"
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include = false
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[fd3509e5-e3ba-409d-ac3d-a9ac84d13296]
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description = "different characters may have the same bytes"
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include = false

‎exercises/practice/anagram/impl.mips

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# | Register | Usage | Type | Description |
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# | -------- | ------------ | ------- | -------------------------------------------------------------- |
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# | `$a0` | input | address | null-terminated target string, without newline |
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# | `$a1` | input | address | null-terminated candidates string with newline after each word |
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# | `$a2` | input/output | address | null-terminated output string with newline after each word |
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# | `$t0-9` | temporary | any | for temporary storage |
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.globl find_anagrams
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find_anagrams:
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jr $ra

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