1 #include <iostream>
2 #include <algorithm>
3 #include <cstdio>
4 using namespace std;
5
6 int a1[4001],a2[4001];
7 int b1[4001],b2[4001];
8 int sum1[4001*4000],sum2[4001*4000];
9
10 int binarySearch(int left,int right,int key)
11 {
12 __int64 ans=0; //64位整数
13 while(left<=right)
14 {
15 int mid = (left + right) / 2;
16 if(sum2[mid] == key)
17 {
18 ans++;
19 for(int i=mid-1; i>=left; i--) //搜到后可能相邻的左边有相等的也满足条件的数！
20 {
21 if(sum2[i]!=key)
22 {
23 break;
24 }
25 ans++;
26 }
27 for(int j=mid+1; j<=right; j++)
28 {
29 if(sum2[j]!=key)
30 {
31 break;
32 }
33 ans++;
34 }
35 return ans;
36 }
37 else if(sum2[mid] < key) left = mid+1;
38 else right = mid -1;
39 }
40 return 0;
41 }
42
43 int main()
44 {
45 int n;
46 cin>>n;
47 __int64 ans=0;
48 for(int i = 0; i < n; i++)
49 {
50 cin>>a1[i]>>a2[i]>>b1[i]>>b2[i];
51
52 }
53 int times = 0;
54 for(int i = 0; i < n; i++) //四数相加转化为两数，通过两两随机相加，以便二分
55 for(int j = 0; j < n; j++)
56 {
57 sum1[times] = a1[i] + a2[j];
58 sum2[times] = b1[i] + b2[j];
59 times++; //加时的下表
60 }
61 sort(sum2,sum2 + times);
62
63 for(int i = 0; i < times; i++)
64 {
65 int key = -sum1[i];
66 ans += binarySearch(0,times-1,key);
67 }
68 cout<<ans<<endl;
69 return 0;
70 }
二分 基础
Time Limit:15000MS Memory Limit:228000KB 64bit IO Format:%I64d & %I64u
Description
The SUM problem can be formulated as follows: given four lists A, B, C, D of integer values, compute how many quadruplet (a, b, c, d ) ∈ A x B x C x D are such that a + b + c + d = 0 . In the following, we assume that all lists have the same size n .
Input
The first line of the input file contains the size of the lists n (this value can be as large as 4000). We then have n lines containing four integer values (with absolute value as large as 2 28 ) that belong respectively to A, B, C and D .
Output
For each input file, your program has to write the number quadruplets whose sum is zero.
Sample Input
6 -45 22 42 -16 -41 -27 56 30 -36 53 -37 77 -36 30 -75 -46 26 -38 -10 62 -32 -54 -6 45
Sample Output
5
Hint
Sample Explanation: Indeed, the sum of the five following quadruplets is zero: (-45, -27, 42, 30), (26, 30, -10, -46), (-32, 22, 56, -46),(-32, 30, -75, 77), (-32, -54, 56, 30).