1510: [POI2006]Kra-The Disks

水题一道不解释，前缀和暴力裸过。。就是不知为什么，poi原数据我总有一个跑不对= =。详见程序

#include<cstdio>
int n,m,x;
int a[400001],b[400001];
int min(int a,int b){return a<b? a:b;}
int main(){
    scanf("%d%d",&n,&m);
    for (int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    b[1]=a[1];
    for (int i=2;i<=n;i++){
        b[i]=min(a[i],b[i-1]);
        //printf("b[%d]=%d\n",i,b[i]);
    }
    int j=n+1,ans=0;
    for (int i=1;i<=m;i++){
        scanf("%d",&x);
        while (b[j]<x&&j>=1) j--;
        if (j>=1) ans=j;
        //printf("%d %d %d\n",x,i,j);
        j--;
    }
    printf("%d\n",ans);
}