題目鏈接

 1 /*
 2     Name:HDU-2141-Can you find it?
 3     Copyright:
 4     Author:
 5     Date: 2018/4/12 17:15:46
 6     Description:
 7         暴力，復雜度n^3,不存在的
 8         將公式變換為A-B=X-C
 9         枚舉A-B，復雜度n^2 
10         二分查找復雜度O(log2n)，A-B是否存在A-B==X-C
11 */
12 #include <iostream>
13 #include <algorithm> 
14
 
 using namespace std;
15 const int MAXN = 1e6 + 10;
16 int a[MAXN], b[MAXN], c[MAXN], ab[MAXN], x[MAXN];
17 int main()
18 {
19 //    freopen("in.txt", "r", stdin);
20     
21     int l, n, m;
22     int cas = 0;
23     while (cin>>l>>n>>m) {
24         cout<<"Case "<<++cas<<"
 
:"<<endl;
25         for (int i=0; i<l; i++) {
26             cin>>a[i];
27         }
28         for (int i=0; i<n; i++) {
29             cin>>b[i];
30         }
31         int k = 0;
32         for (int i=0; i<l; i++) {
33             for(int j=0; j<n; j++) {
34                 ab[k++] = a[i] + b[j];
 
35             }
36         }
37         k--;
38         sort(ab, ab+k);
39         for (int i=0; i<m; i++) {
40             cin>>c[i];
41         }
42         int s;
43         cin>>s;
44         for (int i=0; i<s; ++i) {
45             cin>>x[i];
46         }
47         for (int i=0; i<s; i++) {
48             int flag = 0;
49             for (int j=0; j<m; ++j) {
50                 int tmp = x[i] - c[j];
51                 if (binary_search(ab, ab+k, tmp) == true) {
52                     flag = 1;
53                     break;
54                 }
55             }
56             if (flag) cout<<"YES"<<endl;
57             else cout<<"NO"<<endl;
58         }
59     }
60     return 0;
61 }

hdoj-2141-Can you find it?