Path Sum 深度搜索

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.

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Tree Depth-first Search

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool hasPathSum(TreeNode *root, int sum) {

        if(root==NULL)        //路不通
            return false;
        if(sum-root->val==0 && root->left==NULL && root->right==NULL)    //结束条件
            return true;
        if(hasPathSum(root->left,sum-root->val))
            return true;
        else
            return hasPathSum(root->right,sum-root->val);
    }
};