202410151601
tags: #hash-map

var fourSumCount = function(nums1, nums2, nums3, nums4) {
	const map = new Map();
	for (const n1 of nums1) {
		for (const n2 of nums2) {
			const sum = n1 + n2;
			map.set(sum, (map.get(sum) ?? 0) + 1);
		}
	}
	let res = 0;
	for (const n3 of nums3) {
		for (const n4 of nums4) {
			const sum = n3 + n4;
			if (map.has(-sum)) {
				res += map.get(-sum);
			}
		}
	}
	return res;
};

Reference

https://leetcode.com/problems/4sum-ii/