4Sum II

Description

Given four lists A, B, C, D of integer values, compute how many tuples (i, j, k, l) there are such that A[i] + B[j] + C[k] + D[l] is zero.

To make problem a bit easier, all A, B, C, D have same length of N where 0 ≤ N ≤ 500. All integers are in the range of -2²⁸ to 2²⁸ - 1 and the result is guaranteed to be at most 2³¹ - 1.

Example:

Input:
A = [ 1, 2]
B = [-2,-1]
C = [-1, 2]
D = [ 0, 2]
Output:
2
Explanation:
The two tuples are:

(0, 0, 0, 1) -> A[0] + B[0] + C[0] + D[1] = 1 + (-2) + (-1) + 2 = 0
(1, 1, 0, 0) -> A[1] + B[1] + C[0] + D[0] = 2 + (-1) + (-1) + 0 = 0

 

Solution(javascript)

/**
 * @param {number[]} A
 * @param {number[]} B
 * @param {number[]} C
 * @param {number[]} D
 * @return {number}
 */
var fourSumCount = function(A, B, C, D) {
    const map1 = {}
   for(let i = 0; i < A.length; i++) {
       for(let j = 0; j < B.length; j++) {
           const sum = A[i] + B[j]
           map1[sum] = (map1[sum] || 0) + 1
       }
   }
    let count = 0
    for(let i = 0; i < C.length; i++) {
       for(let j = 0; j < D.length; j++) {
           const sum = C[i] + D[j]
            if(map1[-sum]) {
                count += map1[-sum]
            }
       }
   }
    return count
};