0129. Sum Root to Leaf Numbers.cpp

// 129.✅ Sum Root to Leaf Numbers

/*
You are given the root of a binary tree containing digits from 0 to 9 only.

Each root-to-leaf path in the tree represents a number.

For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123.
Return the total sum of all root-to-leaf numbers. Test cases are generated so that the answer will fit in a 32-bit integer.

A leaf node is a node with no children.

 

Example 1:


Input: root = [1,2,3]
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
Example 2:


Input: root = [4,9,0,5,1]
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.
*/

class Solution {
public:
    void sum(TreeNode *root, int val, int& res)
    {
        int curr = val * 10 + root->val;
        if(root->left == NULL && root->right == NULL)
        {
            //leaf node
            res += curr;
            return;
        }
        if(root->left !=  NULL)
            sum(root->left,curr,res);
        if(root->right != NULL)
            sum(root->right,curr,res);
    }
    
    int sumNumbers(TreeNode* root) {
        if(root == NULL)
            return 0;
        int res = 0;
        
        sum(root,0,res);
        
        return res;
    }
};