二分查找 HDOJ 2141 Can you find it?

题目传送门

 1 /*
 2      题意：给出一个数，问是否有ai + bj + ck == x
 3      二分查找：首先计算sum[l] = a[i] + b[j]，对于q，枚举ck，查找是否有sum + ck == x
 4 */
 5 #include <cstdio>
 6 #include <algorithm>
 7 #include <cmath>
 8 using namespace std;
 9
10 typedef long long ll;
11 const int MAXN = 5e2 + 10;
12 const int INF = 0x3f3f3f3f;
13 ll a[MAXN], b[MAXN], c[MAXN];
14 ll sum[MAXN*MAXN];
15 int tot;
16
17 bool my_binary_search(int l, int r, ll k)   {
18     while (l < r)   {
19         int mid = (l + r) >> 1;
20         if (sum[mid] == k)  return true;
21         else if (sum[mid] > k)  r = mid;
22         else    l = mid + 1;
23     }
24     return false;
25 }
26
27 int main(void)  {       //HDOJ 2141 Can you find it?
28     //freopen ("HDOJ_2141.in", "r", stdin);
29
30     int l, n, m, s, cas = 0;
31     while (scanf ("%d%d%d", &l, &n, &m) == 3)   {
32         for (int i=1; i<=l; ++i)    scanf ("%I64d", &a[i]);
33         for (int i=1; i<=n; ++i)    scanf ("%I64d", &b[i]);
34         for (int i=1; i<=m; ++i)    scanf ("%I64d", &c[i]);
35         scanf ("%d", &s);
36
37         printf ("Case %d:\n", ++cas);
38         sort (a+1, a+1+l);  sort (b+1, b+1+n);  sort (c+1, c+1+m);
39         tot = 0;
40         for (int i=1; i<=l; ++i)    {
41             for (int j=1; j<=n; ++j)    {
42                 sum[++tot] = a[i] + b[j];
43             }
44         }
45         sort (sum+1, sum+1+tot);
46
47         ll mn = a[1] + b[1] + c[1], mx = a[l] + b[n] + c[m];
48         while (s--) {
49             ll q;  scanf ("%I64d", &q);
50             if (q < mn || q > mx)   {
51                 puts ("NO");    continue;
52             }
53             bool flag = false;
54             for (int i=1; i<=m; ++i)    {
55                 int p = lower_bound (sum+1, sum+1+tot, q - c[i]) - sum;
56                 if (p < 1 || p > tot)   continue;
57                 if (sum[p] + c[i] == q) {
58                     flag = true;    puts ("YES");   break;
59                 }
60                 //if (my_binary_search (1, tot, q - c[i]))    {
61                     //flag = true;    puts ("YES");   break;
62                 //}
63             }
64             if (!flag)  {
65                 puts ("NO");
66             }
67         }
68     }
69
70     return 0;
71 }