60分求优化

#include <bits/stdc++.h>
#define ll long long
#define endl "\n"
using namespace std;
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n, m;
    cin >> n >> m;
    char a[n + 5][m + 5];
    for (int i = 1;i <= n;i++){
        for (int j = 1;j <= m;j++){
            cin >> a[i][j];
        }
    }
    while (1){
        bool flag = true;
        for (int i = 1;i <= n;i++){
            for (int j = 1;j <= m;j++){
                if (a[i][j] >= 'A' && a[i][j] <= 'Z'){
                    if (a[i + 1][j] == '.'){
                        a[i + 1][j] = a[i][j];
                        a[i][j] = '.';
                        flag = false;
                    }
                }
            }
        }
        if (flag){
            break;
        }
    }
    for (int i = 1;i <= n;i++){
        for (int j = 1;j <= m;j++){
            cout << a[i][j];
        }
        cout << endl;
    }
    return 0;
}