Kamen

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

struct pos {
    int y, x;
    pos(int Y, int X)
    {
        y = Y;
        x = X;
    }
};

#define N 30100
#define M 35

char board[N][M];
vector<pos> path[M];
int n, m;

int empty(int y, int x)
{
    return board[y][x] == '.';
}

void gen(int y, int x, vector<pos> &vec)
{
    vec.push_back(pos(y, x));
    if (y == n || board[y + 1][x] == 'X') {
        return ;
    }
    if (empty(y + 1, x)) {
        gen(y + 1, x, vec);
    }
    else {
        if (empty(y, x - 1) && empty(y + 1, x - 1)) {
            gen(y + 1, x - 1, vec);
        }
        else if (empty(y, x + 1) && empty(y + 1, x + 1)) {
            gen(y + 1, x + 1, vec);
        }
    }
}

int main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= m; ++j) {
            cin >> board[i][j];
        }
    }
    for (int j = 1; j <= m; ++j) {
        gen(1, j, path[j]);
    }
    int amt;
    cin >> amt;
    for (int it = 1; it <= amt; ++it) {
        int x;
        cin >> x;
        #define k path[x].back()
        while (board[k.y][k.x] == 'O') {
            path[x].pop_back();
        }
        pos z = path[x].back();
        path[x].pop_back();
        gen(z.y, z.x, path[x]);
        assert(board[k.y][k.x] == '.');
        board[k.y][k.x] = 'O';
    }
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= m; ++j) {
            cout << board[i][j];
        }
        cout << "\n";
    }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED