[LeetCode]Path Sum

题目解析:(链接)

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.

解题思路：

深度优先搜索

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool dfs(TreeNode *root, int sum, int cur_sum) {
        if (!root) {
            return false;
        }
        
        if (root->left == nullptr && root->right == nullptr) {
            return sum == cur_sum + root->val;
        }
        
        return dfs(root->left, sum, cur_sum + root->val) || dfs(root->right, sum, cur_sum + root->val);
    }
    
    bool hasPathSum(TreeNode* root, int sum) {
        return dfs(root, sum, 0);
    }
};