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.

For example:

Given the below binary tree and

1
sum = 22

,

1
2
3
4
5
6
7
8
      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.

深度优先搜索就可以了.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
/**
 * 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 hasPathSum(TreeNode* root, int sum) {
        return DFS(root, 0, sum);
    }
    
    bool DFS(TreeNode *node, int n, int sum){
        if(!node){
            return false;
        }
        if(!node->left && !node->right){
            if(n + node->val == sum)
                return true;
            else
                return false;
        }
        if(!node->left && node->right){
            return DFS(node->right, node->val + n, sum);
        }
        if(node->left && !node->right){
            return DFS(node->left, node->val + n, sum);
        }
        if(node->left && node->right){
            return DFS(node->left, node->val + n, sum) || DFS(node->right, node->val + n, sum);
        }
    }
};