LeetCode 437: Path Sum III Solution
Master LeetCode problem 437 (Path Sum III), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.
437. Path Sum III
Problem Explanation
Explanation:
To solve this problem, we can use a recursive approach where we traverse the binary tree and at each node, we check all possible paths starting from that node. We keep track of the running sum along the path from the root to the current node. At each step, we check if the running sum equals the target sum and count such paths. We also recursively explore the left and right subtrees to find paths starting from those nodes.
Steps:
- Implement a recursive function that traverses the tree and checks for paths with the given sum.
- At each node, check if the running sum equals the target sum and update the count accordingly.
- Recursively call the function for the left and right children with updated running sum.
- Return the total count of paths found.
Time Complexity: O(n^2) in the worst case where n is the number of nodes in the tree. Space Complexity: O(n) for the recursive stack.
:
Solution Code
class Solution {
public int pathSum(TreeNode root, int targetSum) {
if (root == null) return 0;
return pathSumFrom(root, targetSum) + pathSum(root.left, targetSum) + pathSum(root.right, targetSum);
}
private int pathSumFrom(TreeNode node, int targetSum) {
if (node == null) return 0;
int count = 0;
if (node.val == targetSum) count++;
count += pathSumFrom(node.left, targetSum - node.val);
count += pathSumFrom(node.right, targetSum - node.val);
return count;
}
}Try It Yourself
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