二叉树篇

 easy.

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {private int ret=Integer.MIN_VALUE;public int maxPathSum(TreeNode root) {dfs(root);return ret;}private int dfs(TreeNode node){if(node==null){return 0;}int lVal=dfs(node.left);int rVal=dfs(node.right);ret=Math.max(ret,lVal+rVal+node.val);return Math.max(Math.max(lVal,rVal)+node.val,0);}
}