poj3264RMQ

区间最值。学了下 st算法，o(1)的查询，这个要比线段树犀利。而且线段树的log(n)前面的常数也比较大。

#include<iostream>
#include<cstdio>
#include<cstring>

using namespace std;

int n, q;
const int maxn = 111111;
int dp[maxn][20];
int dp1[maxn][20];
int a[maxn];
void gao()
{
    for (int i = 0; i < n; i++)
        dp[i][0] = a[i];
    for (int j = 1; (1 << j) <= n; j++){
        for (int i = 0; i + (1 << j) - 1 < n; i++){
            dp[i][j] = min(dp[i][j - 1], dp[i + (1 << (j-1))][j - 1]);
        }
    }
}

int ask(int l, int r)
{
    int k = 0;
    while ((1 << (k + 1)) <= r - l + 1) k++;
    return min(dp[l][k], dp[r-(1<<k)+1][k]);
}

void gao1()
{
    memset(dp1,0,sizeof(dp1));
    for (int i = 0; i < n; i++)
        dp1[i][0] = a[i];
    for (int j = 1; (1 << j) <= n; j++){
        for (int i = 0; i + (1 << j) - 1 < n; i++){
            dp1[i][j] = max(dp1[i][j - 1], dp1[i + (1 << (j-1))][j - 1]);
        }
    }
}

int ask1(int l, int r)
{
    int k = 0;
    while ((1 << (k + 1)) <= r - l + 1) k++;
    return max(dp1[l][k], dp1[r + 1 - (1 << k)][k]);
}

int main()
{
    int l, r;
    while (cin >> n >> q){
        for (int i = 0; i < n; i++)
            scanf("%d",&a[i]);
        gao(); gao1();
        for (int i = 0; i < q; i++){
            scanf("%d%d",&l,&r);
            l--;r--;
            printf("%d
",ask1(l,r)- ask(l,r));
        }
    }
    return 0;
}