附上一個詳細的大佬的講解 http://blog.csdn.net/niushuai666/article/details/6624672

RMQ模板（NYOJ 119）

#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <vector>
#include <algorithm>
#include <cmath>
using namespace std;
const int MAXN=1e5+10;
int
 
 a[MAXN];
int maxsum[MAXN][20];
int minsum[MAXN][20];
int maxx;
int minn;
void RMQ_In(int num) //預處理->O(nlogn)
{
    for(int j = 1; j < 20; ++j)
        for(int i = 1; i <= num; ++i)
            if(i + (1 << j) - 1 <= num)
            {
                maxsum[i][j] = max(maxsum[i][j - 1
 
], maxsum[i + (1 << (j - 1))][j - 1]);
                minsum[i][j] = min(minsum[i][j - 1], minsum[i + (1 << (j - 1))][j - 1]);
            }
}
void RMQ_Query(int src,int des)
{
        int k=(int)(log(des-src+1.0)/log(2.0));
        maxx=max(maxsum[src][k],maxsum[des-(1<<k)+1][k]);
        minn
 
=min(minsum[src][k],minsum[des-(1<<k)+1][k]);
}
int main()
{
   int n,q,a,b;
    scanf("%d%d",&n,&q);
    for(int i=1;i<=n;i++){
        scanf("%d",&minsum[i][0]);
        maxsum[i][0]=minsum[i][0];
    }
    RMQ_In(n);
    while(q--)
    {
        scanf("%d%d",&a,&b);
        RMQ_Query(a,b);
        printf("%d\n",maxx-minn);
    }
    return 0;
}

RMQ模板