437. Path Sum III (Easy)
https://leetcode.com/problems/path-sum-iii/
You are given a binary tree in which each node contains an integer value.
Find the number of paths that sum to a given value.
The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).
The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.
Example:
root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8 10 / \ 5 -3 / \ \ 3 2 11 / \ \ 3 -2 1 Return 3. The paths that sum to 8 are: 1. 5 -> 3 2. 5 -> 2 -> 1 3. -3 -> 11
Solutions
class Solution {
public int pathSum(TreeNode root, int sum) {
// keep the track of visiting path
LinkedList<Integer> path = new LinkedList<>();
return traverse(root, path, sum);
}
private int traverse(TreeNode root, LinkedList<Integer> path, int target) {
int ans = 0;
if (root == null) {
return ans;
}
path.add(root.val);
int sum = 0;
int len = path.size();
for (int i = len - 1; i >= 0; i--) {
sum += path.get(i);
if (sum == target) {
ans++;
// do not break once found, there may contains 0 values that brings in another combination
}
}
ans += traverse(root.left, path, target);
ans += traverse(root.right, path, target);
path.removeLast();
return ans;
}
}