Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5             / \            4   8           /   / \          11  13  4         /  \      \        7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */  bool dfs(TreeNode *root,int ans,int sum){     if(root){         if(root->left==NULL && root->right==NULL){             if(ans+root->val==sum) return true;             else         return false;         }         else{             bool flag1=dfs(root->left,ans+root->val,sum);             bool flag2=dfs(root->right,ans+root->val,sum);             return flag1||flag2;         }     }     else      return false; } class Solution {public:    bool hasPathSum(TreeNode *root, int sum) {        return dfs(root,0,sum);    }};