【LeetCode】Path Sum II

题意

Given a binary tree and a sum, find all root-to-leaf paths where each path’s sum equals the given sum.

思路

基本的深搜，注意一点就是必须是根到叶子节点求和，不可在非叶子节点处停。

代码

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int> > pathSum(TreeNode *root, int sum) {
        vector<vector<int> > result;
        vector<int> re;
        if (!root)  return result;
        dfs(result,re,root,sum);
        return result;
    }
    void dfs(vector<vector<int> >&result,vector<int> &re,TreeNode *cur,int sum){
        if (sum==cur->val){
            if (!cur->left&&!cur->right){       //判断是否为叶子节点
                re.push_back(cur->val);
                result.push_back(re);
                re.pop_back();
                return;
            }
        }
        if (cur->left){                         //递归左孩子
            re.push_back(cur->val);
            dfs(result,re,cur->left,sum-cur->val);
            re.pop_back();
        }
        if (cur->right){                        //递归右孩子
            re.push_back(cur->val);
            dfs(result,re,cur->right,sum-cur->val);
            re.pop_back();
        }
    }
};