Leetcode no. 124

最新推荐文章于 2020-08-06 10:39:54 发布

SmithZz

最新推荐文章于 2020-08-06 10:39:54 发布

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本文介绍了一个解决二叉树最大路径和问题的算法。该算法通过递归方式遍历二叉树，找到从任意节点开始到任意节点结束的最大路径和。实现中使用了双返回值技巧，分别记录单边最大路径和与全局最大路径和。

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124. Binary Tree Maximum Path Sum

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.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxPathSum(TreeNode root) {
        return iterate(root)[1];
    }
    private int[] iterate(TreeNode root){
        int[] res= {0, Integer.MIN_VALUE};
        if (root== null) return res;
        int[] left= iterate(root.left);
        int[] right= iterate(root.right);
        int Single= Math.max(left[0], right[0])+ root.val;
        res[0]= Math.max(Single, 0);
        int Max= Math.max(left[1], right[1]);
        res[1]= Math.max(Max, left[0]+right[0]+root.val);
        return res;
    }
}