C. Letters （前缀和二分查找）

Posted 2022-04-03 -ackerman

题目链接：http://codeforces.com/problemset/problem/978/C

 

题目的意思：告诉你几个宿舍，然后每个宿舍有多少个房间，每个房间的编号是一次从第一个加起来的，现在给你一些信封，信封上只有房间号，现在让我们判断这个房间是属于哪个宿舍，在这个宿舍里他是第几个房间。 

 

第一种方法手写二分：

 1 #include <cstdio>
 2 #include <string>
 3 #include <iostream>
 4 #include <algorithm>
 5 #include <cstdbool>
 6 #include <string.h>
 7 #include <math.h>
 8 
 9 
10 using namespace std;
11 
12 typedef long long LL;
13 
14 LL a[2000005];
15 LL pre[2000005];
16 
17 LL binarySearch(LL a[],LL n,LL key)
18 
19     LL left = 1,right = n-1;
20     while (left <= right)
21     
22         LL mid = (left + right) / 2;
23         if (a[mid] >= key)
24             right = mid - 1;
25         else if (a[mid] < key)
26             left = mid + 1;
27     
28     return left;
29 
30 
31 int main()
32 
33     ios_base::sync_with_stdio(0);
34     cin.tie(NULL);
35     LL n,m;
36     cin >> n >> m;
37     for (LL i=1;i<=n;i++)
38     
39         cin >> a[i];
40         pre[i] = pre[i-1]+a[i];
41     
42     LL temp;
43     for (LL i=1;i<=m;i++)
44     
45         cin >> temp;
46         LL pos = binarySearch(pre,n,temp);
47         cout << pos << ‘ ‘ << temp-pre[pos-1] << endl;
48     
49     return 0;
50 

 

第二种方法：利用C++的函数

 1 #include <cstdio>
 2 #include <string>
 3 #include <iostream>
 4 #include <algorithm>
 5 #include <cstdbool>
 6 #include <string.h>
 7 #include <math.h>
 8 
 9 
10 using namespace std;
11 
12 typedef long long LL;
13 
14 LL a[2000005];
15 LL pre[2000005];
16 
17 
18 int main()
19 
20     ios_base::sync_with_stdio(0);
21     cin.tie(NULL);
22     LL n,m;
23     cin >> n >> m;
24     for (LL i=1;i<=n;i++)
25     
26         cin >> a[i];
27         pre[i] = pre[i-1]+a[i];
28     
29     LL temp;
30     for (LL i=1;i<=m;i++)
31     
32         cin >> temp;
33         LL pos = lower_bound(pre+1,pre+1+n,temp)-pre;
34         cout << pos << ‘ ‘ << temp-pre[pos-1] << endl;
35     
36     return 0;
37