LeetCode 124 Binary Tree Maximum Path Sum

题目链接：

https://leetcode.com/problems/binary-tree-maximum-path-sum/description/

Given a non-empty 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 must contain at least one node and does not need to go through the root.

Example 1:

Example 2:

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dfs 深度遍历

遍历的时候，记录根节点到左子树和右子树中的某个点的最大距离，再比较下即可

class Solution {
public:
    int ans = -99999999;
    int maxPathSum(TreeNode* root) {
      
        dfs(root);
        return ans;
    }
    
    int dfs(TreeNode* root)
    {
        if(root->left==NULL&&root->right==NULL)
        {  ans=max(ans,root->val);return root->val;}
        if(root->left!=NULL&&root->right==NULL)
        {
            int xleft = dfs(root->left);
            ans = max(ans,max(root->val+xleft,root->val));
            return max(root->val+xleft,root->val);
        }
        if(root->left==NULL&&root->right!=NULL)
        {
            int xright = dfs(root->right);
            ans = max(ans,max(root->val,root->val+xright));
            return max(root->val,root->val+xright);
        }
        if(root->left!=NULL&&root->right!=NULL)
        {
            int xleft = dfs(root->left);
            int xright = dfs(root->right);
            ans = max(ans,max(root->val,max(root->val+xleft,max(root->val+xleft+xright,root->val+xright))));
            return max(root->val,max(root->val+xleft,root->val+xright));
        }
    }
    
    
};