## Algorithm

Problem Name: 454. 4Sum II

Given four integer arrays `nums1`, `nums2`, `nums3`, and `nums4` all of length `n`, return the number of tuples `(i, j, k, l)` such that:

• `0 <= i, j, k, l < n`
• `nums1[i] + nums2[j] + nums3[k] + nums4[l] == 0`

Example 1:

```Input: nums1 = [1,2], nums2 = [-2,-1], nums3 = [-1,2], nums4 = [0,2]
Output: 2
Explanation:
The two tuples are:
1. (0, 0, 0, 1) -> nums1[0] + nums2[0] + nums3[0] + nums4[1] = 1 + (-2) + (-1) + 2 = 0
2. (1, 1, 0, 0) -> nums1[1] + nums2[1] + nums3[0] + nums4[0] = 2 + (-1) + (-1) + 0 = 0
```

Example 2:

```Input: nums1 = [0], nums2 = [0], nums3 = [0], nums4 = [0]
Output: 1
```

Constraints:

• `n == nums1.length`
• `n == nums2.length`
• `n == nums3.length`
• `n == nums4.length`
• `1 <= n <= 200`
• `-228 <= nums1[i], nums2[i], nums3[i], nums4[i] <= 228`

## Code Examples

### #1 Code Example with Java Programming

```Code - Java Programming```

``````
class Solution {
public int fourSumCount(int[] A, int[] B, int[] C, int[] D) {
Map map = new  HashMap<>();
for (int i=0; i < A.length; i++) {
for (int j=0; j < B.length; j++) {
map.put(A[i] + B[j], map.getOrDefault(A[i] + B[j], 0) + 1);
}
}

int ans = 0;

for (int i=0; i < C.length; i++) {
for (int j=0; j < D.length; j++) {
ans += map.getOrDefault(-1 * (C[i] + D[j]), 0);
}
}

return ans;
}
}
``````
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Input

cmd
nums1 = [1,2], nums2 = [-2,-1], nums3 = [-1,2], nums4 = [0,2]

Output

cmd
2

### #2 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
const fourSumCount = function(A, B, C, D) {
const map = new Map()
let res = 0
for (let i = 0, clen = C.length; i  <  clen; i++) {
for (let j = 0, dlen = D.length; j  <  dlen; j++) {
map.set(
C[i] + D[j],
typeof map.get(C[i] + D[j]) == 'undefined'
? 1
: map.get(C[i] + D[j]) + 1
)
}
}
for (let i = 0, alen = A.length; i  <  alen; i++) {
for (let j = 0, blen = B.length; j  <  blen; j++) {
res +=
typeof map.get((A[i] + B[j]) * -1) == 'undefined'
? 0
: map.get((A[i] + B[j]) * -1)
}
}
return res
}
``````
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Input

cmd
nums1 = [1,2], nums2 = [-2,-1], nums3 = [-1,2], nums4 = [0,2]

Output

cmd
2

### #3 Code Example with Python Programming

```Code - Python Programming```

``````
class Solution:
def fourSumCount(self, A: List[int], B: List[int], C: List[int], D: List[int]) -> int:
ab = collections.Counter([a + b for a in A for b in B])
return sum(-c - d in ab and ab[-c-d] for c in C for d in D)
``````
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Input

cmd
nums1 = [0], nums2 = [0], nums3 = [0], nums4 = [0]

Output

cmd
1

### #4 Code Example with C# Programming

```Code - C# Programming```

``start coding...``
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