Thieves and Prisons

input/code.cpp: In function 'int main()':
input/code.cpp:75:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (fre.size() != P) {
         ~~~~~~~~~~~^~~~

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

#if DEBUG
#include "prettyprint.hpp"
#define PRINTLN(x) \
    cerr << x << "\n"
#define PRINTSP(x) \
    cerr << x << " "
#else
#define PRINTLN(x)
#define PRINTSP(x)
#endif

#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define PI 3.141592653589793238462643

template<class T> void amax(T & a, const T & b) { a = max(a,b); }
template<class T> void amin(T & a, const T & b) { a = min(a,b); }


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int N, P, M;
    cin >> N >> P >> M;
    vector<pair<char, int>> eve (M);
    for (int m=0; m < M; m++) {
        char c; int a;
        cin >> c >> a;
        eve[m] = {c, a-1};
    }
    vector<int> res (M, -1);
    queue<int> fre;
    map<int, int> fil;      // time, num
    for (int p=1; p <= P; p++) {
        fre.push(p);
    }
    vector<int> tned (N, M+5);
    int nxtop = M+4, nxtopp = 1;
    for (int m=M-1; m >= 0; m--) {
        int th = eve[m].second;
        if (eve[m].first == 'C') {
            if (tned[th] < nxtop) {
                cout << "IMPOSSIBLE\n";
                return 0;
            }
            auto it = fil.lower_bound(tned[th]);
            if (it != fil.begin()) {
                it--;
                fre.push((*it).second);
                res[m] = (*it).second;
                fil.erase(it);
            }
            else {
                res[m] = nxtopp;
            }
        }
        else {      // O
            tned[th] = m;
            if (fre.empty()) {
                cout << "IMPOSSIBLE\n";
                return 0;
            }
            res[m] = fre.front();
            fre.pop();
            fil.insert({m, res[m]});
            nxtop = m;
            nxtopp = res[m];
        }
    }

    if (fre.size() != P) {
        cout << "IMPOSSIBLE\n";
        return 0;
    }

    for (int m=0; m < M; m++) {
        cout << res[m] << " ";
    }
}

Test 1

Group: 2, 4, 5

Verdict: ACCEPTED

Test 2

Group: 2, 4, 5

Verdict: ACCEPTED

Test 3

Group: 2, 4, 5

Verdict: WRONG ANSWER

Test 4

Group: 2, 4, 5

Verdict: ACCEPTED

Test 5

Group: 2, 4, 5

Verdict: ACCEPTED

Test 6

Group: 4, 5

Verdict: ACCEPTED

Test 7

Group: 4, 5

Verdict: ACCEPTED

Test 8

Group: 4, 5

Verdict: ACCEPTED

Test 9

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 10

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 11

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 12

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 13

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 14

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 15

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 16

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 17

Group: 1, 2, 3, 4, 5

Verdict: ACCEPTED

Test 18

Group: 1, 3, 4, 5

Verdict: ACCEPTED

Test 19

Group: 2, 5

Verdict: ACCEPTED

Test 20

Group: 2, 5

Verdict: ACCEPTED

Test 21

Group: 2, 5

Verdict: ACCEPTED

Test 22

Group: 5

Verdict: ACCEPTED

Test 23

Group: 5

Verdict: ACCEPTED

Test 24

Group: 3, 4, 5

Verdict: ACCEPTED

Test 25

Group: 3, 4, 5

Verdict: ACCEPTED

Test 26

Group: 3, 4, 5

Verdict: ACCEPTED

Test 27

Group: 3, 4, 5

Verdict: ACCEPTED

Test 28

Group: 4, 5

Verdict: ACCEPTED

Test 29

Group: 4, 5

Verdict: ACCEPTED

Test 30

Group: 4, 5

Verdict: ACCEPTED

Test 31

Group: 4, 5

Verdict: ACCEPTED

Test 32

Group: 2, 4, 5

Verdict: ACCEPTED

Test 33

Group: 2, 4, 5

Verdict: ACCEPTED

Test 34

Group: 2, 4, 5

Verdict: ACCEPTED

Test 35

Group: 2, 4, 5

Verdict: ACCEPTED

Test 36

Group: 3, 5

Verdict: ACCEPTED

Test 37

Group: 3, 5

Verdict: ACCEPTED

Test 38

Group: 3, 5

Verdict: ACCEPTED

Test 39

Group: 3, 5

Verdict: ACCEPTED

Test 40

Group: 5

Verdict: ACCEPTED

Test 41

Group: 5

Verdict: ACCEPTED

Test 42

Group: 5

Verdict: ACCEPTED

Test 43

Group: 5

Verdict: ACCEPTED

Test 44

Group: 2, 5

Verdict: ACCEPTED

Test 45

Group: 2, 5

Verdict: ACCEPTED

Test 46

Group: 2, 5

Verdict: ACCEPTED

Test 47

Group: 2, 5

Verdict: ACCEPTED