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  • Binary Tree Maximum Path Sum

    Binary Tree Maximum Path Sum

    Total Accepted: 55016 Total Submissions: 246213 Difficulty: Hard

    Given a binary tree, find the maximum path sum.

    For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path does not need to go through the root.

    For example:
    Given the below binary tree,

           1
          / 
         2   3

    Return 6.

     
    设最大路径和为sum , 那么sum = max(sum,左子树根出发的最大路径和+根结点的值+右子树根出发的最大路径和);
    根据这个式子写成递归式就可以了
    有一点需要注意,如果从左右子树根出发的最大路径和为负数,那么将其值置0,因为根的值+从左右子树根出发的最大路径和 一定会小于根的值
    /**
     * 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:
        int maxPathSum(TreeNode *root) {
            int maxPath = INT_MIN;
            maxPathWithNode(root,maxPath);
            return maxPath;
        }
        int maxPathWithNode(TreeNode* node,int& maxPath){
            if(!node) return 0;
            int l = max(0,maxPathWithNode(node->left,maxPath));
            int r = max(0,maxPathWithNode(node->right,maxPath));
            maxPath = max(maxPath,l+r+node->val);
           // cout<<"node->val="<<node->val<<" l="<<l<<" r="<<r<<" maxPath="<<maxPath<<endl;
            return max(l,r)+node->val;
        }
    };
    /*
    [-1,-2,-3,4,-5,-6,-7,8,-9,-1,-1,-1,-1,-1,-1,-7,-8]
    [-9,-9]
    */
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  • 原文地址:https://www.cnblogs.com/zengzy/p/5056777.html
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