Description
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
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| 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
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Solution
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class Solution {
private int res = 0;
public int pathSum(TreeNode root, int sum) {
if (root == null) return 0;
HashMap<Integer, Integer> presum = new HashMap<>();
presum.put(0, 1);
helper(presum, root, 0, sum);
return res;
}
private void helper(HashMap<Integer, Integer> presum, TreeNode node, int cur, int target){
if (node == null) return;
cur = cur + node.val;
if (presum.getOrDefault(cur - target, 0) > 0){
res += presum.get(cur - target);
}
presum.put(cur, presum.getOrDefault(cur, 0) + 1);
helper(presum, node.left, cur, target);
helper(presum, node.right, cur, target);
presum.put(cur, presum.get(cur) - 1);
}
}
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