ICPC 国内予選 2014 C

main.cpp

#include <iostream>
#include <cmath>
#include <climits>
#include <algorithm>
#include <iomanip>
#include <vector>

using namespace std;

int main()
{
    int r; int n;
    while (cin >> r >> n, r | n) {
        vector<int> citySunRising(40, 0); // 0: 20
        for (int i = 0; i < n; ++i) {
            int xl, xr, h;
            cin >> xl >> xr >> h;
            for (int j = xl; j < xr; ++j) {
                citySunRising[j + 20] = max(h, citySunRising[j + 20]);
            }
        }

        double ans = DBL_MAX;
        for (int i = -r; i < 0; ++i) {
            ans = min(ans, r - r * sin(acos((i + 1) / (double)r)) + citySunRising[i + 20]);
        }
        for (int i = 0; i < r; ++i) {
            ans = min(ans, r - r * sin(acos((i) / (double)r)) + citySunRising[i + 20]);
        }
        cout << fixed << setprecision(4) << ans << endl;

    }

    return 0;
}