package code;

import java.util.HashMap;

/*
 * 437. Path Sum III
 * sum
 * Easy
 * Tree
 * khashmap. 
 * Tips dfs 
 *       ==0+==sum
 *       lc560
 *       Easy
 *       lc112, lc113, lc437, lc129, lc124, lc337
 *       lc437 lc572 
 *       lc303, lc437, lc560
 */
public class lc437 {
    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) {
            val = x;
        }
    }


    public static int pathSum(TreeNode root, int sum) { //
        if (root == null) return 0;
        return dfs(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum);
    }

    public static int dfs(TreeNode root, int sum) { //
        if (root == null) return 0;
        if (root.val == sum) return 1 + dfs(root.left, sum - root.val) + dfs(root.right, sum - root.val);//10
        return dfs(root.left, sum - root.val) + dfs(root.right, sum - root.val);
    }


    public static int pathSum2(TreeNode root, int sum) {//k
        if (root == null) return 0;
        HashMap hs = new HashMap();
        hs.put(0, 1);
        return helper(root, sum, hs, 0);
    }
    public static int helper(TreeNode root, int sum, HashMap hs, int cur_sum) {
        if (root == null)
            return 0;
        cur_sum += root.val;
        int res = hs.getOrDefault(cur_sum - sum, 0);    //
        hs.put(cur_sum, hs.getOrDefault(cur_sum, 0)+1);     //
        res += helper(root.left, sum, hs, cur_sum);     //
        res += helper(root.right, sum, hs, cur_sum);
        hs.put(cur_sum, hs.get(cur_sum)-1);
        return res;
    }
}