poj 3061 尺取法或二分

 

经典尺取法，复杂度O(n)。

 1 #include <iostream>

 2 #include <cstring>

 3 #include <cstdio>

 4 using namespace std;

 5 

 6 const int INF = 999999;

 7 const int N = 100000;

 8 int a[N];

 9 

10 int main ()

11 {

12     int t;

13     scanf("%d", &t);

14     while ( t-- )

15     {

16         int n, s;

17         scanf("%d%d", &n, &s);

18         for ( int i = 0; i < n; i++ ) scanf("%d", a + i);

19         int p = 0, q = 0, sum = 0, len = INF;

20         while ( 1 )

21         {

22             while ( q < n && sum < s )

23             {

24                 sum += a[q++];

25             }

26             if ( sum < s ) break;

27             len = min( len, q - p );

28             sum -= a[p++];

29         }

30         if ( len == INF ) len = 0;

31         printf("%d\n", len);

32     }

33     return 0;

34 }

二分也可以做，复杂度多了个log。

 1 #include <algorithm>

 2 #include <iostream>

 3 #include <cstring>

 4 #include <cstdio>

 5 using namespace std;

 6 

 7 typedef long long ll;

 8 const int INF = 999999;

 9 const int N = 100001;

10 ll sum[N];

11 

12 int main ()

13 {

14     int t;

15     scanf("%d", &t);

16     while ( t-- )

17     {

18         int n, s;

19         scanf("%d%d", &n, &s);

20         sum[0] = 0;

21         for ( int i = 1; i <= n; i++ )

22         {

23             scanf("%lld", sum + i);

24             sum[i] += sum[i - 1];

25         }

26         int len = INF;

27         for ( int i = n; i > 0; i-- )

28         {

29             if ( sum[i] < s ) break;

30             int pos = upper_bound( sum, sum + i, sum[i] - s ) - sum;

31             if ( pos != i )

32             {

33                 len = min( len, i - pos + 1 );

34             }

35         }

36         if ( len == INF ) len = 0;

37         printf("%d\n", len);

38     }

39     return 0;

40 }