[leetcode]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.

不用多说，递归周游即可。

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root == NULL)
            return false;
        return DepthFirst(root,0,sum);

    }
    bool DepthFirst(TreeNode *root,int s,int sum)
    {
        if(root->left == NULL && root->right == NULL)
        {
            if(s + root->val == sum)
                return true;
            else
                return false;
        }
        if(root->left != NULL)
        {
            bool leftResult;
            leftResult = DepthFirst(root->left,s+root->val,sum);
            if(leftResult == true)
                return true;
        }
        if(root->right != NULL)
        {
            bool rightResult;
            rightResult = DepthFirst(root->right,s+root->val,sum);
            if(rightResult == true)
                return true;
        }
        return false;
    }
};