Submission #1203416

#	Time	Username	Problem	Language	Result	Execution time	Memory
1203416		javkhlantugs0504	Finding Routers (IOI20_routers)	C++20	0 / 100	1 ms	324 KiB

routers

#include <vector>
#include <algorithm>

// Provided by the grader — DO NOT implement yourself!
int use_detector(int x);

// You must implement this
std::vector<int> find_routers(int l, int n, int q) {
    std::vector<int> positions(n);
    positions[0] = 0; // router 0 is always at position 0

    for (int i = 1; i < n; ++i) {
        // Binary search: leftmost position where use_detector(x) == i
        int lo = 0, hi = l, left = -1;
        while (lo <= hi) {
            int mid = (lo + hi) / 2;
            int res = use_detector(mid);
            if (res < i) {
                lo = mid + 1;
            } else {
                if (res == i) left = mid;
                hi = mid - 1;
            }
        }

        // Binary search: rightmost position where use_detector(x) == i
        lo = 0, hi = l;
        int right = -1;
        while (lo <= hi) {
            int mid = (lo + hi) / 2;
            int res = use_detector(mid);
            if (res > i) {
                hi = mid - 1;
            } else {
                if (res == i) right = mid;
                lo = mid + 1;
            }
        }

        // Estimate router position as the center of its range, rounded down to even
        int pos = ((left + right) / 2) & ~1;
        positions[i] = pos;
    }

    return positions;
}

• Subtask 1: 0 / 16
• Subtask 2: 0 / 21
• Subtask 3: 0 / 23
• Subtask 4: 0 / 40