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54 lines (43 loc) · 1.46 KB
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package com.fishercoder.solutions;
import java.util.HashMap;
import java.util.Map;
/**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:
1. (0, 0, 0, 1) -> A[0] + B[0] + C[0] + D[1] = 1 + (-2) + (-1) + 2 = 0
2. (1, 1, 0, 0) -> A[1] + B[1] + C[0] + D[0] = 2 + (-1) + (-1) + 0 = 0*/
public class _454 {
public static int fourSumCount(int[] A, int[] B, int[] C, int[] D) {
Map<Integer, Integer> map = new HashMap();
int result = 0;
int len = A.length;
for (int i = 0; i < len; i++) {
for (int j = 0; j < len; j++) {
int sum = A[i] + B[j];
if (map.containsKey(sum)) {
map.put(sum, map.get(sum) + 1);
} else {
map.put(sum, 1);
}
}
}
for (int i = 0; i < len; i++) {
for (int j = 0; j < len; j++) {
int sum = -(C[i] + D[j]);
if (map.containsKey(sum)) {
result += map.get(sum);
}
}
}
return result;
}
}