二分模板

https://www.acwing.com/problem/content/791/

#include<bits/stdc++.h>
using namespace std;
const int N = 1e5 + 15;
int n, m, x;
int a[N];

int main() {
    ios::sync_with_stdio(0); 
    cin.tie(0);

    cin >> n >> m;
    for(int i = 0; i < n; i++) cin >> a[i];

    while(m--) {
        cin >> x;
        int l = 0, r = n - 1;
        while(l < r) {
            int mid = l + r >> 1;
            if(a[mid] >= x) r = mid;
            else l = mid + 1;
        }
        if(a[l] != x) cout << "-1 -1" << endl;
        else {
            cout << l << " ";
            l = 0, r = n - 1;
            while(l < r) {
                int mid = l + r + 1 >> 1;
                if(a[mid] <= x) l = mid;
                else r = mid - 1;
            }
            cout << r << endl;
        }
    }
    return 0;
}

https://www.acwing.com/problem/content/792/

#include<bits/stdc++.h>
using namespace std;

int main() {
    // ios::sync_with_stdio(0); 
    // cin.tie(0);

    double n;
    cin >> n;
    double l = -100, r = 100;
    while(abs(l - r) > 1e-8) {
        double mid = (l + r) / 2;
        if(mid * mid * mid > n) r = mid;
        else l = mid;
    }
    printf("%.6lf", l);
    return 0;
}