POJ 3264 Balanced Lineup

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>

using namespace std;

const int MAX = 50000;
const int INF = 1e9;
struct node{
    int l, r, up, down;
    int mid(){
        return (l + r) >> 1;
    }
}tree[MAX << 2];

int Max,Min;
void buildtree(int l, int r, int rt){
    tree[rt].l = l;
    tree[rt].r = r;
    if(l == r){
        scanf("%d",&tree[rt].up);
        tree[rt].down = tree[rt].up;
        return;
    }
    int mid = tree[rt].mid();
    buildtree(l, mid, rt << 1);
    buildtree(mid + 1, r, rt << 1 | 1);
    tree[rt].up = max(tree[rt << 1].up, tree[rt << 1 | 1].up);
    tree[rt].down = min(tree[rt << 1].down, tree[rt << 1 | 1].down);
}

void query(int l, int r, int rt){
    if(tree[rt].l >= l && tree[rt].r <= r){

        Max = max(tree[rt].up, Max);
        Min = min(tree[rt].down, Min);
        return;
    }
    int mid = tree[rt].mid();
    if(r <= mid)    query(l, r, rt << 1);
    else if(l > mid)    query(l, r, rt << 1 | 1);
    else{
        query(l, mid, rt << 1), query(mid + 1, r, rt << 1 | 1);
    }
}

int main(){
//    freopen("in.txt", "r", stdin);
    int N,Q;
    while(scanf("%d%d",&N,&Q) != EOF){
        buildtree(1, N, 1);
        int l,r;
        for(int i=0; i<Q; i++){
            scanf("%d%d",&l,&r);
            Min = INF;
            Max = -INF;
            query(l, r, 1);
            printf("%d\n",Max - Min);
        }
    }
    return 0;
}