BZOJ 4590: [Shoi2015]自动刷题机 二分答案

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 #define inf 233333333;
 6 using namespace std;
 7 int n,k;
 8 long long a[100001];
 9 long long l,r,ans_l,ans_r,mid;
10 int i;
11 long long cnt=0;
12 long long num,maxn;
13 long long check(long long x)
14 {
15     int i;
16     long long sum=0; 
17     long long num=0;
18     for (i=1;i<=n;i++) {
19       sum+=a[i];
20       if (sum<0) sum=0;
21       else {
22           if (sum>=x) {
23               num++;
24               sum=0;
25           }
26       }
27     }
28     return num;
29 }
30 int main()
31 {
32     scanf("%d%d",&n,&k);
33     for (i=1;i<=n;i++) {
34         scanf("%lld",&a[i]);
35         if (a[i]>0) num+=a[i];
36     }
37     maxn=num;
38     l=1; r=maxn; 
39     while (l<=r) {
40         mid=(l+r)>>1;
41         //cout<<mid<<endl;
42         if (check(mid)>k)  l=mid+1;
43         else r=mid-1;
44     }
45     ans_l=l;
46     l=1; r=maxn; 
47     while (l<=r) {
48         mid=(l+r)>>1;
49         //cout<<mid<<endl;
50         if (check(mid)<k)  r=mid-1;
51         else l=mid+1;
52     }
53     ans_r=r;    
54     if (check(ans_l)!=k||check(ans_r)!=k) printf("%d",-1);
55     else printf("%lld %lld",ans_l,ans_r);
56 }