# Path Sum III

Category

Binary Tree - DFS

Checkbox

Checkbox

Difficulty

Medium

Index

36

Key Ideas

The key idea to solve problem 437, Path Sum III, is to perform a depth-first search on the binary tree and keep track of the prefix sum at each node, then check if the current prefix sum minus the target sum exists in a hashmap of prefix sums encountered so far.

Problem Number

437

Problem Summary

The problem "Path Sum III" is a medium difficulty problem in the Binary Tree - DFS category on LeetCode. It involves finding the number of paths in a binary tree that sum up to a given target value. Key pitfalls to watch out for include properly tracking the sum in each path, considering both the left and right subtrees, and handling negative values in the tree nodes.

Solution Summary

The best solution for solving the "Path Sum III" problem in LeetCode-75 curated list involves using depth-first search (DFS) on the binary tree. The algorithm traverses each node in the tree and calculates the sum of paths starting from that node. At each node, it recursively searches for paths that sum up to the target value. To achieve this, the algorithm maintains a running sum and a hashmap that stores the frequency of previously encountered sums. By incrementing the count of the running sum in the hashmap and exploring both the left and right subtrees, the algorithm can find the number of paths that sum up to the target value. The solution has a time complexity of O(n), where n is the number of nodes in the tree.

Tags

Tree

Depth-First Search