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
给定四个包含整数的数组列表 A , B , C , D ,计算有多少个元组 (i, j, k, l) ，使得 A[i] + B[j] + C[k] + D[l] = 0。
为了使问题简单化，所有的 A, B, C, D 具有相同的长度 N，且 0 ≤ N ≤ 500 。所有整数的范围在 -228 到 228 - 1 之间，最终结果不会超过 231 - 1 。
例如:
输入: A = [ 1, 2] B = [-2,-1] C = [-1, 2] D = [ 0, 2] 输出: 2 解释: 两个元组如下: 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
264ms
1 class Solution {
2 func fourSumCount(_ A: [Int], _ B: [Int], _ C: [Int], _ D: [Int]) -> Int {
3 var map: [Int: Int] = [:]
4 for i in 0..<A.count {
5 for j in 0..<B.count {
6 let sum = A[i] + B[j]
7 map[sum, default: 0] += 1
8 }
9 }
10
11 var count = 0
12 for i in 0..<C.count {
13 for j in 0..<D.count {
14 let sum = C[i]+D[j]
15 if let negativeOfSum = map[-sum] {
16 count += negativeOfSum
17 }
18 }
19 }
20
21 return count
22 }
23 }
312ms
1 class Solution {
2 func fourSumCount(_ A: [Int], _ B: [Int], _ C: [Int], _ D: [Int]) -> Int {
3 var map: [Int: Int] = [:]
4 for i in A.indices {
5 for j in B.indices {
6 map[A[i] + B[j], default: 0] += 1
7 }
8 }
9
10 var result = 0
11 for i in C.indices {
12 for j in D.indices {
13 result += map[-C[i]-D[j], default:0]
14 }
15 }
16
17 return result
18 }
19 }
436ms
1 class Solution {
2 func Max(_ A: ([Int], Int), _ B: ([Int], Int)) -> ([Int], Int) {
3 if A.0.count > B.0.count {
4 return A
5 }else{
6 return B
7 }
8 }
9 func Min(_ A: ([Int], Int), _ B: ([Int], Int)) -> ([Int], Int) {
10 if A.0.count < B.0.count {
11 return A
12 }else{
13 return B
14 }
15 }
16 func fourSumCount(_ A: [Int], _ B: [Int], _ C: [Int], _ D: [Int]) -> Int {
17 var nums = [A, B, C, D]
18 let A1 = Max(Max((nums[0],0), (nums[1],1)), Max((nums[2],2), (nums[3],3)))
19 nums.remove(at: A1.1)
20 let B1 = Min(Min((nums[0],0), (nums[1],1)), (nums[2], 2))
21 nums.remove(at: B1.1)
22 let C1 = nums[0]
23 let D1 = nums[1]
24
25 var dict = [Int:Int]()
26 for a in A1.0 {
27 for b in B1.0 {
28 if let n = dict[a + b]{
29 dict[a + b] = n + 1
30 }else{
31 dict[a + b] = 1
32 }
33 }
34 }
35 var count = 0
36 for c in C1 {
37 for d in D1 {
38 if let n = dict[0 - c - d] {
39 count += n
40 }
41 }
42 }
43 return count
44 }
45 }
540ms
1 class Solution {
2 func fourSumCount(_ A: [Int], _ B: [Int], _ C: [Int], _ D: [Int]) -> Int {
3 var res:Int = 0
4 var n:Int = A.count
5 var m1:[Int:Int] = [Int:Int]()
6 var m2:[Int:Int] = [Int:Int]()
7 for i in 0..<n
8 {
9 for j in 0..<n
10 {
11 if m1[A[i] + B[j]] == nil
12 {
13 m1[A[i] + B[j]] = 1
14 }
15 else
16 {
17 m1[A[i] + B[j]]! += 1
18 }
19 if m2[C[i] + D[j]] == nil
20 {
21 m2[C[i] + D[j]] = 1
22 }
23 else
24 {
25 m2[C[i] + D[j]]! += 1
26 }
27 }
28 }
29 for (key,val) in m1
30 {
31 if m2[-key] != nil
32 {
33 res += val * m2[-key]!
34 }
35 }
36 return res
37 }
38 }
548ms
1 class Solution {
2 func fourSumCount(_ A: [Int], _ B: [Int], _ C: [Int], _ D: [Int]) -> Int {
3 var result = 0
4 var map: [Int: Int] = [:]
5 for a in A {
6 for b in B {
7 let sum = a + b
8 if let count = map[sum] {
9 map[sum] = count + 1
10 } else {
11 map[sum] = 1
12 }
13 }
14 }
15
16 for c in C {
17 for d in D {
18 let sum = -(c + d)
19 if let count = map[sum] {
20 result += count
21 }
22 }
23 }
24
25 return result
26 }
27 }
880ms
1 class Solution {
2 func fourSumCount(_ A: [Int], _ B: [Int], _ C: [Int], _ D: [Int]) -> Int {
3
4 var res = 0
5
6 var CDRecord = [Int : Int]()
7
8 for c in C {
9 for d in D {
10 if let r = CDRecord[c + d] {
11 CDRecord[c + d] = r + 1
12 } else {
13 CDRecord[c + d] = 1
14 }
15 }
16 }
17
18 for a in A {
19 for b in B {
20 let complete = 0 - (a + b)
21
22 if let value = CDRecord[complete] {
23 res += value
24 }
25 }
26 }
27 return res
28 }
29 }