第六周：[Leetcode]112. 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.

进行DFS，注意一定是要到叶子节点的路径之和，非叶子节点的不算。

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

bool dfs(TreeNode* p, int sum){
if(p == NULL)
return false;
sum -= p -> val;
if((sum == 0) && (p -> left == NULL) && (p -> right == NULL))
return true;
return dfs(p -> left, sum) || dfs(p -> right,sum);
}
};