[LeetCode]Binary Tree Maximum Path Sum, 解题报告

• 左子树路径和 = 递归查找左子树
• 右子树路径和 = 递归查找右子树
• 如果 左子树路径和 + 右子树路径和 + 当前节点值 > 当前最大路径和，则更新当前最大路径和

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private static int maxValue;
    
    public static int maxPathSum(TreeNode root) {
        maxValue = root == null ? 0 : root.val;
        findPath(root);
        return maxValue;
    }
    
    public static int findPath(TreeNode root) {
        if (root == null) {
            return 0;
        }
        
        int left = Math.max(findPath(root.left), 0);
        int right = Math.max(findPath(root.right), 0);
        
        maxValue = Math.max(maxValue, root.val + left + right);
        
        int current = Math.max(root.val, Math.max(root.val + left, root.val + right));
                
        return current;
    }
}