DSU on tree

static const int maxn = 1e5 + 5;

vector <int> graph[maxn];
int color[maxn], subtreeSize[maxn], cnt[maxn];
bool big[maxn];

// Calculate size of the subtree of every vertices
void dfs(int u, int p = -1)
{
    subtreeSize[u] = 1; // Every vertex has itself in its subtree
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        dfs(v, u);
        subtreeSize[u] += subtreeSize[v]; // Add size of child v to its parent(v)
    }
}

void add(int u, int p, int x)
{
    cnt[ color[u] ] += x;
    for (int v : graph[u])
    {
        if (v != p || big[v])
            continue;
        add(v, u, x);
    }
}

void dsu(int u, int p, bool keep)
{
    int mx(-1), bigChild(-1);
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        if (subtreeSize[v] > mx)
        {
            mx = subtreeSize[v];
            bigChild = v;
        }
    }
    for (int v : graph[u])
    {
        if (v == p || v == bigChild)
            continue;
        dsu(v, u, 0); // Run a dfs from small child and clear them from cnt
    }
    if (bigChild != -1)
    {
        dsu(bigChild, u, 1);
        big[bigChild] = 1; // bigChild marked as big and not cleared from cnt
    }
    add(u, p, 1);
    // cnt[c] is the number of vertices in subtree of vertex u that has color c.
    if (bigChild != -1)
        big[bigChild] = 0;
    if (keep == 0)
        add(u, p, -1); // remove
}   static const int maxn = 1e5 + 5;

vector <int> graph[maxn];
int color[maxn], subtreeSize[maxn], cnt[maxn];
bool big[maxn];

// Calculate size of the subtree of every vertices
void dfs(int u, int p = -1)
{
    subtreeSize[u] = 1; // Every vertex has itself in its subtree
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        dfs(v, u);
        subtreeSize[u] += subtreeSize[v]; // Add size of child v to its parent(v)
    }
}

void add(int u, int p, int x)
{
    cnt[ color[u] ] += x;
    for (int v : graph[u])
    {
        if (v != p || big[v])
            continue;
        add(v, u, x);
    }
}

void dsu(int u, int p, bool keep)
{
    int mx(-1), bigChild(-1);
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        if (subtreeSize[v] > mx)
        {
            mx = subtreeSize[v];
            bigChild = v;
        }
    }
    for (int v : graph[u])
    {
        if (v == p || v == bigChild)
            continue;
        dsu(v, u, 0); // Run a dfs from small child and clear them from cnt
    }
    if (bigChild != -1)
    {
        dsu(bigChild, u, 1);
        big[bigChild] = 1; // bigChild marked as big and not cleared from cnt
    }
    add(u, p, 1);
    // cnt[c] is the number of vertices in subtree of vertex u that has color c.
    if (bigChild != -1)
        big[bigChild] = 0;
    if (keep == 0)
        add(u, p, -1); // remove
}   static const int maxn = 1e5 + 5;

vector <int> graph[maxn];
int color[maxn], subtreeSize[maxn], cnt[maxn];
bool big[maxn];

// Calculate size of the subtree of every vertices
void dfs(int u, int p = -1)
{
    subtreeSize[u] = 1; // Every vertex has itself in its subtree
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        dfs(v, u);
        subtreeSize[u] += subtreeSize[v]; // Add size of child v to its parent(v)
    }
}

void add(int u, int p, int x)
{
    cnt[ color[u] ] += x;
    for (int v : graph[u])
    {
        if (v != p || big[v])
            continue;
        add(v, u, x);
    }
}

void dsu(int u, int p, bool keep)
{
    int mx(-1), bigChild(-1);
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        if (subtreeSize[v] > mx)
        {
            mx = subtreeSize[v];
            bigChild = v;
        }
    }
    for (int v : graph[u])
    {
        if (v == p || v == bigChild)
            continue;
        dsu(v, u, 0); // Run a dfs from small child and clear them from cnt
    }
    if (bigChild != -1)
    {
        dsu(bigChild, u, 1);
        big[bigChild] = 1; // bigChild marked as big and not cleared from cnt
    }
    add(u, p, 1);
    // cnt[c] is the number of vertices in subtree of vertex u that has color c.
    if (bigChild != -1)
        big[bigChild] = 0;
    if (keep == 0)
        add(u, p, -1); // remove
}   static const int maxn = 1e5 + 5;

vector <int> graph[maxn];
int color[maxn], subtreeSize[maxn], cnt[maxn];
bool big[maxn];

// Calculate size of the subtree of every vertices
void dfs(int u, int p = -1)
{
    subtreeSize[u] = 1; // Every vertex has itself in its subtree
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        dfs(v, u);
        subtreeSize[u] += subtreeSize[v]; // Add size of child v to its parent(v)
    }
}

void add(int u, int p, int x)
{
    cnt[ color[u] ] += x;
    for (int v : graph[u])
    {
        if (v != p || big[v])
            continue;
        add(v, u, x);
    }
}

void dsu(int u, int p, bool keep)
{
    int mx(-1), bigChild(-1);
    for (int v : graph[u])
    {
        if (v == p)
            continue;
        if (subtreeSize[v] > mx)
        {
            mx = subtreeSize[v];
            bigChild = v;
        }
    }
    for (int v : graph[u])
    {
        if (v == p || v == bigChild)
            continue;
        dsu(v, u, 0); // Run a dfs from small child and clear them from cnt
    }
    if (bigChild != -1)
    {
        dsu(bigChild, u, 1);
        big[bigChild] = 1; // bigChild marked as big and not cleared from cnt
    }
    add(u, p, 1);
    // cnt[c] is the number of vertices in subtree of vertex u that has color c.
    if (bigChild != -1)
        big[bigChild] = 0;
    if (keep == 0)
        add(u, p, -1); // remove
}