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
Solution:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int pathSum(TreeNode root, int sum) {
Map<Integer,Integer> map = new HashMap<>();
map.put(0,1);
return helper(root, 0, sum, map);
}
public int helper(TreeNode root, int pre, int tar, Map<Integer,Integer> map){
if(root==null) return 0;
pre += root.val;
int ans = map.getOrDefault(pre-tar,0);
map.put(pre, map.getOrDefault(pre,0)+1);
ans += helper(root.left, pre, tar, map) + helper(root.right, pre, tar, map);
map.put(pre, map.get(pre)-1);
return ans;
}
}