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124.binary-tree-maximum-path-sum.cpp
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64 lines (58 loc) · 1.74 KB
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// Tag: Dynamic Programming, Tree, Depth-First Search, Binary Tree
// Time: O(N)
// Space: O(H)
// Ref: -
// Note: -
// A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.
// The path sum of a path is the sum of the node's values in the path.
// Given the root of a binary tree, return the maximum path sum of any non-empty path.
//
// Example 1:
//
//
// Input: root = [1,2,3]
// Output: 6
// Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.
//
// Example 2:
//
//
// Input: root = [-10,9,20,null,null,15,7]
// Output: 42
// Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.
//
//
// Constraints:
//
// The number of nodes in the tree is in the range [1, 3 * 104].
// -1000 <= Node.val <= 1000
//
//
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
int res = INT_MIN;
int maxPathSum(TreeNode* root) {
helper(root);
return res;
}
int helper(TreeNode *node) {
if (!node) {
return 0;
}
int left = max(helper(node->left), 0);
int right = max(helper(node->right), 0);
res = max(res, left + right + node->val);
return max(left, right) + node->val;
}
};