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.

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 Tree Depth-first Search

思路：记录从根节点到所有叶子节点的路径和，然后判断sum是否在路径和中

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    set<int> res;    void function(TreeNode* root,int num)    {        if(root==NULL)            res.insert(num);        else{            int temp=num+root->val;            if(root->left==NULL&&root->right==NULL)                function(root->left,temp);            else if(root->left==NULL&&root->right!=NULL)                function(root->right,temp);            else if(root->left!=NULL&&root->right==NULL)                function(root->left,temp);            else{                function(root->left,temp);                function(root->right,temp);            }        }            }    bool hasPathSum(TreeNode *root, int sum) {        if(root==NULL)            return false;        function(root,0);        set<int>::iterator it=res.find(sum);        if(it==res.end())            return false;        else            return true;    }};