Cinte's Leetcode Record
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124. Binary Tree Maximum Path Sum

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Symbols count in article: 1.3k Reading time ≈ 1 mins.

124. Binary Tree Maximum Path Sum

和543. Diameter of Binary Tree很像
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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxPathSum(TreeNode* root) {
        int curMax = INT_MIN;
        helper(root, curMax);
        return curMax;
    }
private:
    int helper(TreeNode* node, int& curMax)
    {
        if(!node)
            return 0;

        auto left = helper(node->left, curMax);
        auto right = helper(node->right, curMax);
        auto curSum = (left < 0 ? 0 : left) + (right < 0 ? 0 :right) + node->val;
        curMax = max(curSum, curMax);
        return max(max(left, right), 0) + node->val;

        return 0;
    } 
};

稍微改改，思想没变，但可以少1次的判断 

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class Solution {
public:
    int maxPathSum(TreeNode* root) {
        int curMax = INT_MIN;
        helper(root, curMax);
        return curMax;
    }
private:
    int helper(TreeNode* node, int& curMax)
    {
        if(!node)
            return 0;
        auto left = max(helper(node->left, curMax), 0);
        auto right = max(helper(node->right, curMax), 0);
        auto curSum = left + right + node->val;
        curMax = max(curSum, curMax);
        return max(left, right) + node->val;
    } 
};