一维st表-poj3264

区间最值问题，

倍增+动态规划的思想

适用于不更新节点且询问次数多

#include <cstdio>
#include <cmath>
#include <algorithm>

using namespace std;

int maxn[50001][30], minn[50001][30];//i为起点，(1 << j)为区间长度

void init_st(int n);

int main()
{
    int i, j;
    int n, q;
    int x, y;
    scanf("%d %d", &n, &q);
    for(i = 1; i <= n; ++i)//初始化
    {
        scanf("%d", &maxn[i][0]);
        minn[i][0] = maxn[i][0];
    }
    init_st(n);
    for(i = 1; i <= q; ++i)
    {
        scanf("%d %d", &x, &y);
        if(y < x) swap(x, y);
        int k = (int)(log(double(y - x + 1)) / log(2.0));//询问
        int t1 = max(maxn[x][k], maxn[y - (1 << k) + 1][k]);
        int t2 = min(minn[x][k], minn[y - (1 << k) + 1][k]);
        printf("%d\n", t1 - t2);
    }
    return 0;
}

void init_st(int n)
{
    int i, j;
    for(j = 1; j <= (int)log2(n); ++j)
        for(i = 1; i <= n; ++i)
    {
        int tag = i + (1 << j) - 1;
        if(tag > n) continue;
        maxn[i][j] = max(maxn[i][j - 1], maxn[i + (1 << (j - 1))][j - 1]);
        minn[i][j] = min(minn[i][j - 1], minn[i + (1 << (j - 1))][j - 1]);
    }
}