NC_6_TREE_MAX_PATH

package org.example.interview.practice;

import java.util.Objects;

/**
 * @author xianzhe.ma
 * @date 2021/8/18
 */

public class NC_6_TREE_MAX_PATH {

    int maxSum = Integer.MIN_VALUE;
    public int maxPathSum (TreeNode root) {
        // write code here
        maxGain(root);
        return maxSum;
    }
    public int maxGain(TreeNode node) {
        if (node == null) {
            return 0;
        }

        // 递归计算左右子节点的最大贡献值
        // 只有在最大贡献值大于 0 时，才会选取对应子节点
        int leftGain = Math.max(maxGain(node.left), 0);
        int rightGain = Math.max(maxGain(node.right), 0);

        // 节点的最大路径和取决于该节点的值与该节点的左右子节点的最大贡献值
        int priceNewpath = node.val + leftGain + rightGain;

        // 更新答案
        maxSum = Math.max(maxSum, priceNewpath);

        // 返回节点的最大贡献值
        return node.val + Math.max(leftGain, rightGain);
    }

    public int maxGain2(TreeNode node) {
        if (Objects.isNull(node)) {
            return 0;
        }

        int left = Math.max(maxGain2(node.left),0);
        int right = Math.max(maxGain2(node.right),0);

        int currentMax = node.val + left + right;

        maxSum = Math.max(maxSum, currentMax);

        return node.val + Math.max(left, right);
    }

    public class TreeNode {
        int val = 0;
        TreeNode left = null;
        TreeNode right = null;
    }

}