簡單題，求區間最大值和最小值

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define N 1000010
int n,a[N];
int ans_x, ans_y;
struct node
{
    int r,l;
    int maxx,minn;
}s[N<<2];
void build(int l, int r, int n)
{
    s[n].l = l;
    s[n].r = r;
    s[n].maxx = 0;
    s[n].minn = N;
    if(l == r)
    {
        s[n].maxx = s[n].minn = a[l];
        return;
    }
    int mid = (l + r) >> 1;
    build(l, mid, n<<1);
    build(mid + 1, r, n<<1|1);
    s[n].maxx = max(s[n<<1].maxx, s[n<<1|1].maxx);
    s[n].minn = min(s[n<<1].minn, s[n<<1|1].minn);
}
void query(int l, int r, int n)
{
    if(s[n].l == l && s[n].r == r)
    {
        ans_x = max(ans_x, s[n].maxx);
        ans_y = min(ans_y, s[n].minn);
        return;
    }
    int mid = (s[n].l + s[n].r) >> 1;
    if(r <= mid)
        query(l, r, n<<1);
    else if(l > mid)
        query(l, r, n<<1|1);
    else
    {
        query(l, mid, n<<1);
        query(mid+1, r, n<<1|1);
    }
}
int main()
{
    int m,t,i,x,y;
    while(~scanf("%d%d",&m,&t))
    {
        for(i = 1; i <= m; i ++)
            scanf("%d",&a[i]);
        build(1,m,1);
        while(t--)
        {
            scanf("%d%d",&x,&y);
            ans_x = 0;
            ans_y = N;
            query(x,y,1);
            printf("%d\n",ans_x-ans_y);
        }
    }
    return 0;
}