RMQ 的ST表做法

//做法一：ST表查询#define _CRT_SECURE_NO_WARNINGS#include<cstdio>#include<algorithm>#include<cmath>using namespace std;const int N = 100010;int maxsum[20][N], minsum[20][N]; //优化1void RMQ(int num) //预处理->O(nlogn){for (int i = 1; i != 20; ++i)for (int j = 1; j <= num; ++j)if (j + (1 << i) - 1 <= num){maxsum[i][j] = max(maxsum[i - 1][j], maxsum[i - 1][j + (1 << i >> 1)]); //优化2minsum[i][j] = min(minsum[i - 1][j], minsum[i - 1][j + (1 << i >> 1)]);}}int main(){int num, query;int src, des;scanf("%d %d", &num, &query);for (int i = 1; i <= num; ++i) //输入信息处理{scanf("%d", &maxsum[0][i]);minsum[0][i] = maxsum[0][i];}RMQ(num);while (query--) //O(1)查询{scanf("%d %d", &src, &des);int k = (int)(log(des - src + 1.0) / log(2.0));int maxres = max(maxsum[k][src], maxsum[k][des - (1 << k) + 1]);int minres = min(minsum[k][src], minsum[k][des - (1 << k) + 1]);printf("%d\n", maxres - minres);}return 0;}