[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.

DFS或者BFS。同时，当本节点是叶子节点才判断和，否则节点为空时返回false

/**
* 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 dfs(TreeNode *node, int sum, int curSum)
{
if (node == NULL)
return false;

if (node->left == NULL && node->right == NULL)
return curSum + node->val == sum;

return dfs(node->left, sum, curSum + node->val) || dfs(node->right, sum, curSum + node->val);
}

bool hasPathSum(TreeNode *root, int sum) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
return dfs(root, sum, 0);
}
};