【POJ】3264 Balanced Lineup

#include<cstdio>
#define MAXN 50010
#define INF 987654321
int a[MAXN<<2],b[MAXN<<2];
inline int MAX(int x,int y)
{
    return x>y?x:y;
}
inline int MIN(int x,int y)
{
    return x>y?y:x;
}
inline void PushUp(int rt)
{
    a[rt]=MAX(a[rt<<1],a[rt<<1|1]);
    b[rt]=MIN(b[rt<<1],b[rt<<1|1]);
}
void Build(int L,int R,int rt)
{
    if(L==R)
    {
        scanf("%d",&a[rt]);
        b[rt]=a[rt];
    }
    else
    {
        int mid=(L+R)>>1;
        Build(L,mid,rt<<1);
        Build(mid+1,R,rt<<1|1);
        PushUp(rt);
    }
}
int Big(int x,int y,int L,int R,int rt)
{
    if(x<=L&&R<=y)
        return a[rt];
    int mid,ans;
    mid=(L+R)>>1;
    ans=-INF;
    if(mid>=x)
        ans=MAX(ans,Big(x,y,L,mid,rt<<1));
    if(y>mid)
        ans=MAX(ans,Big(x,y,mid+1,R,rt<<1|1));
    return ans;
}
int Small(int x,int y,int L,int R,int rt)
{
    if(x<=L&&R<=y)
        return b[rt];
    int mid,ans;
    mid=(L+R)>>1;
    ans=INF;
    if(mid>=x)
        ans=MIN(ans,Small(x,y,L,mid,rt<<1));
    if(y>mid)
        ans=MIN(ans,Small(x,y,mid+1,R,rt<<1|1));
    return ans;
}
int main()
{
    int n,q,x,y;
    while(~scanf("%d%d",&n,&q))
    {
        Build(1,n,1);
        while(q--)
        {
            scanf("%d%d",&x,&y);
            printf("%d\n",Big(x,y,1,n,1)-Small(x,y,1,n,1));
        }
    }
    return 0;
}