Illumination Optimization

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

using pi = pair<int, int>;

void solve() {
    int m, y, n; cin >> m >> y >> n;

    int end = 0, ok = 1, cnt = 0, c = 0;
    for(int i=0; i<n; ++i) {
        int x; cin >> x;
        int l = max(0, x-y), r = min(m, x+y);
        if(l > c) ok = 0;
        if(l > end) {
            cnt ++ ;
            end = c;
        }
        c = r;
    }
    if(end != m) cnt++;
    if(!ok || c != m) cout << "IMPOSSIBLE\n";
    else cout << cnt << '\n';
}

int main() {
    int q; cin >> q;
    for(int i=1; i<=q; ++i) {
        cout << "Case #" << i << ": ";
        solve();
    }
    return 0;
}