optimize sort and remove dups for shrinking

Author: HaoranYi

accounts-db/src/accounts_db.rs

@@ -3908,19 +3908,22 @@ impl AccountsDb {
         // stable sort because we want the most recent only
         accounts.sort_by(|a, b| a.pubkey().cmp(b.pubkey()));
         if accounts.len() > 1 {
-            let mut i = 0;
-            // iterate 0..1 less than end
-            while i < accounts.len() - 1 {
-                let current = accounts[i];
-                let next = accounts[i + 1];
-                if current.pubkey() == next.pubkey() {
-                    // remove the first duplicate
-                    accounts.remove(i);
-                    // do not advance i, we just removed an element at i
-                    continue;
+            let mut last = 0;
+            let mut curr = 1;
+
+            loop {
+                if accounts[curr].pubkey() == accounts[last].pubkey() {
+                    accounts[last] = accounts[curr];
+                } else {
+                    last += 1;
+                    accounts[last] = accounts[curr];
+                }
+                curr += 1;
+                if curr == accounts.len() {
+                    break;
                 }
-                i += 1;
             }
+            accounts.truncate(last + 1);
         }
     }