113. Path Sum II

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

For example:
Given the below binary tree and sum = 22,

              5             / \            4   8           /   / \          11  13  4         /  \    / \        7    2  5   1

return

[   [5,4,11,2],   [5,8,4,5]]

/** * 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:     //这里cur可以用引用，更节省空间，不用引用也可以，如果不用引用，后面cur.pop_back()可以省略。    void pathSum(TreeNode* root,int gap,vector<vector<int>>& result,vector<int> cur){        if(!root) return;        cur.push_back(root->val);        if(!root->left&& !root->right) {            if(root->val==gap) result.push_back(cur);        }        pathSum(root->left,gap-root->val,result,cur);        pathSum(root->right,gap-root->val,result,cur);        cur.pop_back();    }    vector<vector<int>> pathSum(TreeNode* root, int sum) {        vector<vector<int>> result;        std::vector<int> cur;        if(!root) return result;        pathSum(root,sum,result,cur);        return result;    }};

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