poj 3875 RMQ或线段树求区间最值

以前用RMQ做过，刚好最近在做线段树，就用线段树也做了下，1A~

两个域，分别保存当前结点下面的最大值和最小值

View Code

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn = 55555;
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
int MIN[maxn<<2];
int MAX[maxn<<2];
int min(int a,int b){
    return a<b?a:b;
}
int max(int a,int b){
    return a>b?a:b;
}
void pushup(int rt){
    MIN[rt]=min(MIN[rt<<1],MIN[rt<<1|1]);
    MAX[rt]=max(MAX[rt<<1],MAX[rt<<1|1]);
}
void build(int l,int r,int rt)
{
    if(l==r){
        scanf("%d",&MAX[rt]);
        MIN[rt]=MAX[rt];
        return ;
    }
    int m=(l+r)>>1;
    build(lson);build(rson);
    pushup(rt);
}
int query(int L,int R,int l,int r,int rt,bool flag)
{
    if(L <= l && r <= R){
        if(flag) return MAX[rt];
        else return MIN[rt];
    }
    int m=(l+r)>>1;
    int ret1=0,ret2=100000000;
    if(L<=m)
    {
        if(flag) ret1=max(ret1,query(L,R,lson,flag));
         else ret2=min(ret2,query(L,R,lson,flag));
    }
    if(R>m) 
    {
        if(flag) ret1=max(ret1,query(L,R,rson,flag));
        else ret2=min(ret2,query(L,R,rson,flag));
    }
    return flag?ret1: ret2;
}
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        build(1,n,1);
        while(m--)
        {
            int a,b;
            scanf("%d%d",&a,&b);
            int mi=query(a,b,1,n,1,false);
            int mx=query(a,b,1,n,1,true);
            printf("%d\n",mx-mi);
        }
    }
}