HDU 5273 区间DP

Posted 2020-09-18

输入一组数，m次询问

问每一个询问区间的逆序数有多少

区间DP简单题

#include "stdio.h"
#include "string.h"
int dp[1010][1010],a[1010];
int main()
{
    int n,m,i,j,k;

    while (scanf("%d%d",&n,&m)!=EOF)
    {
        for (i=1;i<=n;i++)
            scanf("%d",&a[i]);
        memset(dp,0,sizeof(dp));
        for (i=1;i<=n;i++)
            for (j=1;j+i-1<=n;j++)
            {
                k=i+j-1;
                dp[j][k]=dp[j+1][k]+dp[j][k-1]-dp[j+1][k-1];
                if (a[j]>a[k])
                    dp[j][k]++;
            }
        while (m--)
        {
            scanf("%d%d",&i,&j);
            printf("%d\n",dp[i][j]);
        }
    }
    return 0;
}