学步园

      A sequence of N positive integers (10 < N < 100 000), each of them less than or equal 10000, and a positive integer S (S < 100 000 000) are given. Write a program to find the minimal length of the subsequence of consecutive
elements of the sequence, the sum of which is greater than or equal to S.

尺取法

设置两个指针s,t。

维护一个区间的信息，然后根据指针的移动，更新区间信息。

时间复杂度 O(n).

同类型练习题：

poj 3320  Jessica's Reading Problem

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = 100000 + 100;
int a[maxn];

int main() {
    int T, n, S;
    scanf("%d", &T);
    while(T--)
    {
        scanf("%d%d", &n, &S);
        for(int i=1; i<=n; ++i) scanf("%d", &a[i]);
        int ans = n+1;
        int tmp = 0, s = 1, t = 1;
        while(true)
        {
            while(t<=n && tmp < S) {
                tmp += a[t];
                t++;
            }
            if(tmp < S) break;
            ans = min(ans, t-s);
            tmp -= a[s++];
        }

        if(ans<=n) printf("%d\n", ans);
        else printf("0\n");
    }
    return 0;
}