int find(int x)
{
    if(p[x] != x) p[x] = find(p[x]);
    return p[x];
}
priority_queue<int, vector<int>, greater<int>>

sort(a, a + n, greater<int>())

int primes[N], cnt;
bool st[N];
void get_primes(int n)
{
    for (int i = 2; i <= n; i ++ )
    {
        if(st[i] == false) primes[cnt++] = i;
        for (int j = 0; primse[j] <= n/i; j ++ )
        {
            st[primes[j] * i] = true;
            if(i % primes[j] == 0) break;
        }
    }
}

vector<int> div(vector<int> &A, int B, int r)
{
    vector<int> C;
    for (int i = 0; i < A.size(); i ++ )
    {
        r = r * 10 +A[i];
        C.push_back(r/B);
        r%=B;
    }
    reverse(C.begin(), C.end());
    while(C.size() > 1 && C.back()==0) C.pop();
    return C;
}

bool check(int date)
{
    if(m<=0 || m>12) return false;
    if(d<=0 || m!=2 && d>months[m]) return false;
    if(m==2)
    {
        if(y%4==0 && y%100!=0 || y%400==0)
            months[2] = 29;
        if(d>months[m])
            return false;
    }
    return true;
}

void C()
{
    for (int i = 0; i < N; i ++ )
        for (int j = 0; j <= i; j ++ )
            if(j==0) C[i][j] = 1;
            else C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
}


void primes()
{
    for (int i = 2; i < n/i; i ++ )
    {
        if(n%i==0)
        {
            int cnt = 0;
            while(n%i==0)
            {
                n/=i;
                cnt++;
            }
            printf("%d %d",i, cnt);
        }
    }
    if(n>1) printf("%d %d",n, 1);
}

int e[N], ne[N], idx, h[N];
memset(h, -1, sizeof h);
void add(int a, int b)
{
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx;
    idx ++;
}
void dfs(int u)
{
    for(int i = h[u]; i != -1;i = ne[i])
    {
        int j = e[i];
        if(st[j] == false)
        {
            dfs(j);
        }
    }
}

void maxv()
{
    for (int i = 1; i <= n; i ++ )
    {
        f[i] = 1;
        for (int j = 1; j < i; j ++ )
        {
            if(a[j] < a[i])
                f[i] = max(f[i], f[j] + 1);
        }
    }
}
void maxv()
{
    int n, m;//n为短串, m为长串
    for (int i = 1; i <= n; i ++ )
    {
        for (int j = 1; j <= m; j ++ )
        {
            f[i][j] = max(f[i - 1][j], f[i][j - 1]);
            if(s[i] == s[j])
                f[i][j] = f[i - 1][j - 1] + 1;
        }
    }
}

void bag()
{
    for (int i = 1; i <= n; i ++ )
        for (int j = 0; j <= m; j ++ )
        {
            f[i][j] = f[i - 1][j];
            if(j>=v[i])
                f[i][j] = max(f[i][j], f[i - 1][j - v[i]] + w[i]);
        }
}

void bag()
{
    for (int i = 1; i <= n; i ++ )
        for (int j = 0; j <= m; j ++ )
        {
            f[i][j] = f[i - 1][j];
            if(j>=v[i])
                f[i][j] = max(f[i][j], f[i][j - v[i]] + w[i]);
        }
}

1~26对应a~z,
则要实现数字->字符, 可以
int num = 1; cout << char(num + 'a' - 1);
则要实现字符->数字, 可以
char c = 'b'; cout << c - 'a' + 1;