Binary Tree Maximum Path Sum

发表于

算法：二叉树 + 动态规划

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

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题目

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124. Binary Tree Maximum Path Sum
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:

Input: [1,2,3]

       1
      / \
     2   3

Output: 6
Example 2:

Input: [-10,9,20,null,null,15,7]

   -10
   / \
  9  20
    /  \
   15   7

Output: 42

分析：

不要求 最大值的路径，只要求最大值

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Java解法

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public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}
class Solution {
    int ret = Integer.MIN_VALUE;
    public int maxPathSum(TreeNode root) {
        return maxSum(root);
    }
    public int maxSum(TreeNode root) {
        if (null == root) return 0;
        int l = Math.max(0, maxSum(root.left));
        int r = Math.max(0, maxSum(root.right));
        int sum = l + r + root.val;
        ret = Math.max(ret, sum);
        return Math.max(l, r) + root.val;
    }
}