/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    int total = 0 ;
    public int pathSum(TreeNode root, int target) {
        
        if(root == null){
            return 0;
        }
    
        HashMap<Integer , Integer> preSum = new HashMap<>();
        preSum.put(0,1);
        findPathSum(root , 0 , target , preSum);
        
        return total;
    }
    
    public void findPathSum(TreeNode node ,int sum,int target,HashMap<Integer , Integer> preSum){
        
        if(node == null){
            return ;
        }
        
        sum += node.val;
        
        if(preSum.containsKey(sum - target)){
            total += preSum.get(sum-target);
        }
        
        preSum.put(sum , preSum.getOrDefault(sum,0) + 1);
        
        
        findPathSum(node.left , sum , target , preSum);
        findPathSum(node.right , sum , target , preSum);
        
        preSum.put(sum , preSum.get(sum) - 1);
        
        return;
    }   
}