给定一个非空二叉树,返回其最大路径和。
本题中,路径被定义为一条从树中任意节点出发,达到任意节点的序列。该路径至少包含一个节点,且不一定经过根节点。
示例 1:
输入: [1,2,3] 1 / 2 3 输出: 6
示例 2:
输入: [-10,9,20,null,null,15,7] -10 / 9 20 / 15 7 输出: 42
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
private int max = Integer.MIN_VALUE;
public int maxPathSum(TreeNode root) {
helper(root);
return max;
}
public int helper(TreeNode root)
{
if(root == null) return 0;
int left = helper(root.left);
int right = helper(root.right);
int currSum = Math.max(Math.max(left+root.val, right+root.val), root.val);
int currMax = Math.max(currSum, left+right+root.val);
max = Math.max(currMax, max);
return currSum;
}
}
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int maxPathSum(TreeNode* root) {
int ret = INT_MIN;
onePath(root, ret);
return ret;
}
int onePath(TreeNode *root, int &ret){
if(root == nullptr)
return 0;
int l = onePath(root->left, ret);
int r = onePath(root->right,ret);
ret = max(ret,max(0,l)+max(0,r)+root->val);
return max(0,max(l,r)+root->val);
}
};