Leetcode Problem 437. Path Sum III

437. Path Sum III

Leetcode Solutions

Initialize a counter count to 0 to store the number of valid paths.
Initialize a hashmap h to store the frequency of prefix sums.
Define a recursive function preorder(node, curr_sum) that takes the current node and the current prefix sum as arguments.
Inside preorder, add the value of the current node to curr_sum.
If curr_sum equals the target sum, increment count by 1.
Increment count by the frequency of curr_sum - targetSum from the hashmap.
Increment the frequency of curr_sum in the hashmap by 1.
Recursively call preorder for the left and right children of the current node with the updated curr_sum.
After the recursive calls, decrement the frequency of curr_sum in the hashmap by 1 to avoid counting paths from parallel subtrees.
Return the value of count after the traversal is complete.

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