LeetCode #112 - Path Sum

题目描述：

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.

Note: A leaf is a node with no children.

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.

利用递归遍历二叉树所有可能的路径，判断路径和是否等于目标值。

class Solution {
public:
    bool hasPathSum(TreeNode* root, int sum) {
        int cur=0;
        return hasPathSum_recur(root, cur, sum);
    }
    
    bool hasPathSum_recur(TreeNode* root, int cur, int sum)
    {
        if(root==NULL)  return false;
        else if(root->left==NULL&&root->right==NULL)
        {
            if(cur+root->val==sum) return true;
            else return false;
        }
        cur+=root->val;
        return hasPathSum_recur(root->left,cur,sum)||hasPathSum_recur(root->right,cur,sum);
    }
};