二叉树遍历应用(dfs)124. Binary Tree Maximum Path Sum

canwang_sjtu

于 2016-11-06 16:39:17 发布

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分类专栏： leetcode 文章标签：二叉树

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
// LeetCode, Binary Tree Maximum Path Sum
// 时间复杂度O(n)，空间复杂度O(logn)
class Solution {
public:
    int maxSum = -99999999;

    int maxPathSum(TreeNode *root) {
        if (!root)
            return 0;
        dfs(root);
        return maxSum;
    }

    int dfs(TreeNode *root)
    {
        if (!root)
            return 0;
        int sum = root->val;

        int l = dfs(root->left);
        int r = dfs(root->right);

        if (l>0)
            sum+=l;
        if(r>0)
            sum+=r;
        maxSum = max(sum, maxSum);

        return max(l,r)>0? max(l,r)+root->val: root->val;
    }


};