Path Sum

LeetCode #112

Description:

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.

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.

Idea:

必须要走到leaf才能判断(root->left==NULL && root->right==NULL).这样的话，如果到达root==NULL，那就说明没找着。

[]
0

算是false

Code:

class Solution {
public:
    bool hasPathSum(TreeNode* root, int sum) {
        if(root==NULL) return false;

        if(root->left==NULL && root->right==NULL){
            if(root->val==sum) return true;
        }

        return hasPathSum(root->left, sum-root->val)||hasPathSum(root->right, sum-root->val);
    }

};