[LeetCode] Binary Tree Maximum Path Sum（遞迴）

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Given a binary tree, find the maximum path sum.

The path may start and end at any node in the tree.

For example: Given the below binary tree,

       1      /      2   3

 

Return 6.

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:        int maxPathSum(TreeNode *root) {        if(root==NULL)            return 0;        set<int> s;        return recursion(root,root,s);    }private:    int recursion(TreeNode *p,TreeNode *root,set<int> &s){                int left = 0 ,right=0 ,parent = p->val;        int max = p->val;        if(p->left==NULL && p->right==NULL)            return max;        if(p->left)            left = recursion(p->left,root,s);        if(p->right)            right = recursion(p->right,root,s);        if(left>max && p->left)            s.insert(left);        if(right>max && p->right)            s.insert(right);        if(left+parent>max)            max = left+parent;        if(right+parent>max)            max = right+parent;        if(right+left+parent>max)            s.insert(right+left+parent);        if(p==root && !s.empty()){            set<int>::iterator iter = s.end();            iter--;            return  (max>(*iter)?max:(*iter));        }        return max;    }};