Codeforces Round #771 (Div. 2)

A

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n;
int a[N], b[N];
void solve()
{
    cin >> n;
    for (int i = 1; i <= n; i ++ )  cin >> a[i];
    int pos = 0, pos1 = 0;
    for (int i = 1; i <= n; i ++ ) {
        if (a[i] != i) {
            pos = i;
            break;
        }
    }
    for (int i = 1; i <= n; i ++ ) {
        if (a[i] == pos) {
            pos1 = i;
            break;
        }
    }
    for (int i = pos; i <= (pos1 + pos) / 2; i ++ )
        swap(a[i], a[pos1 - (i - pos)]);
    for (int i = 1; i <= n; i ++ )  cout << a[i] << " ";
    cout << endl;
    return;
}
int main() {
    int T;
    cin >> T;
    while (T -- )   solve();
    return 0;
}

B

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n;
int a[N];
void solve()
{
    cin >> n;
    for (int i = 1; i <= n; i ++ )  cin >> a[i];
    vector<int> b, c;
    for (int i = 1; i <= n; i ++ )
        if (a[i] % 2 == 0)  b.push_back(a[i]);
        else c.push_back(a[i]);
    for (int i = 1; i < b.size(); i ++ )
        if (b[i] < b[i - 1]) {
            puts("NO");
            return;
        }
    for (int i = 1; i < c.size(); i ++ )
        if (c[i] < c[i - 1]) {
            puts("NO");
            return;
        }
    puts("YES");
    return;
}
int main() {
    int T;
    cin >> T;
    while (T -- )   solve();
    return 0;
}

C

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n;
int a[N];
void solve()
{
    cin >> n;
    int res = 0;
    for (int i = 1; i <= n; i ++ )  cin >> a[i];
    for (int i = 1; i <= n; ) {
        if (a[i] == i) {
            i ++;
            res ++;
            continue;
        }
        int j = i + 1;
        vector<int> v;
        v.push_back(a[i]);
        int minn = a[i], maxx = a[i];
        while (j <= n) {
            v.push_back(a[j]);
            minn = min(minn, a[j]);
            maxx = max(maxx, a[j]);
            if (maxx - minn + 1 == v.size() && maxx == j && minn == i) {
                res ++;
                break;
            }
            j ++;
        }
        i = j + 1;
    }
    cout << res << endl;
    return;
}
int main() {
    int T;
    cin >> T;
    while (T -- )   solve();
    return 0;
}

D

#include <bits/stdc++.h>
using namespace std;
const int N = 1010;
int n, m;
int a[N][N];
struct Node {
    int x, y, z;
};
vector<Node> ans;
void dfs(int x, int y)
{
    if (x <= 0 || x >= n || y <= 0 || y >= m)   return;
    int c = 0;
    for (int i = x; i <= x + 1; i ++ ) {
        for (int j = y; j <= y + 1; j ++ ) {
            if (a[i][j]) {
                if (c && c != a[i][j])  return;
                c = a[i][j];
            }
        }
    }
    if (c) {
        ans.push_back({x, y, c});
        for (int i = x; i <= x + 1; i ++ ) 
            for (int j = y; j <= y + 1; j ++ ) 
                a[i][j] = 0;
        for (int i = x - 1; i <= x + 1; i ++ ) 
            for (int j = y - 1; j <= y + 1; j ++ ) 
                dfs(i, j);
    }
}
int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i ++ )  
        for (int j = 1; j <= m; j ++ )
            scanf("%d", &a[i][j]);
    for (int i = 1; i < n; i ++ )
        for (int j = 1; j < m; j ++ )
            dfs(i, j);
    for (int i = 1; i <= n; i ++ ) {
        for (int j = 1; j <= m; j ++ ) {
            if (a[i][j]) {
                printf("-1\n");
                return 0;
            }
        }
    }
    printf("%d\n", ans.size());
    reverse(ans.begin(), ans.end());
    for (auto [x, y, z] : ans)
        printf("%d %d %d\n", x, y, z);
    return 0;
}