HDU-寻找最大值 递推求连续区间

通过枚举每个点作为最小值，再通过动态规划求出以每个点作为最小值的左右区间。

代码如下：

#include <cstring>

#include <cstdio>

#include <cstdlib>

#include <algorithm>

#define MAXN 100005

using namespace std;



typedef long long int Int64;



Int64 seq[MAXN], sum[MAXN], ret;



int L[MAXN], R[MAXN], N;



int main()

{

    while (scanf("%d", &N) == 1) {

        ret = -(1LL << 60);

        for (int i = 1; i <= N; ++i) {

            scanf("%I64d", &seq[i]);    

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

        }

        for (int i = 1; i <= N; ++i) {

            int len = 0, j = i - 1; 

            while (j >= 1) {

                if (seq[j] < seq[i]) break;

                len += L[j] + 1;

                j = i - len - 1;

            }

            L[i] = len;

        }

        for (int i = N; i >= 1; --i) {

            int len = 0, j = i + 1;

            while (j <= N) {

                if (seq[j] < seq[i]) break;

                len += R[j] + 1;

                j = i + len + 1;

            }    

            R[i] = len;

        }

        for (int i = 1; i <= N; ++i) {

            ret = max(ret, (sum[i+R[i]]-sum[i-L[i]-1]) * seq[i]);

        }

        printf("%I64d\n", ret);

    }

    return 0;    

}