一维st表典型题

洛谷p2880

#include <bits/stdc++.h>
const int N = 50010;
int n,q,ans,log_2[N], a[N] = {}, mmin[N][18], mmax[N][18];
using namespace std;
void init() {
    for (int i = 1; i <= n; i++) mmin[i][0] = mmax[i][0] = a[i];
    for (int j = 1; (1 << j) <= n; j++)
        for (int i = 1; i + (1 << j) <= n + 1; i++){ // attention! "+1"
            mmin[i][j] = min(mmin[i][j-1], mmin[i + (1 << j-1)][j-1]);
            mmax[i][j] = max(mmax[i][j-1], mmax[i + (1 << j-1)][j-1]);
            //                                             attention! no "+1"
        }
}
int ai(int l, int r){
    int k = log_2[r-l+1];
    return min(mmin[l][k], mmin[r-(1 << k)+1][k]);
}
int aa(int l, int r){
    int k = log_2[r-l+1];
    return max(mmax[l][k], mmax[r-(1 << k)+1][k]);
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> q;
    for(int i = 1; i <= n; i++) cin >> a[i];
    for(int i = 2; i <= n; i++) log_2[i] = log_2[i >> 1] + 1;
    // attention! i starts from 2
    init();
    while(q--){
        int l , r;
        cin >> l >> r;
        cout << aa(l, r) - ai(l, r) << endl;
    }
    
    
    
    
    return 0;
}