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// 124. Binary Tree Maximum Path Sum
#include "leetcode.h"
/*
* 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 value in the path.
* given the 'root' of a binary tree, return the maximum path sum of any non
* empty path
*/
int dfs(struct TreeNode *root, int *max) {
if (!root)
return 0;
int left = dfs(root->left, max);
int right = dfs(root->right, max);
left = fmax(left, 0);
right = fmax(right, 0);
int curr = left + root->val + right;
*max = fmax(*max, curr);
return root->val + fmax(left, right);
}
int maxPathSum(struct TreeNode *root) {
int ans = INT_MIN;
dfs(root, &ans);
return ans;
}
int main() {
struct TreeNode *root = treenode_create(-10);
root->left = treenode_create(9);
root->right = treenode_create(20);
root->right->left = treenode_create(15);
root->right->right = treenode_create(7);
printf("%d\n", maxPathSum(root)); // expect: 42
}
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