构造

呜呜呜，蒟蒻完全不会构造怎么办

[CF1495C]Garden of the Sun

考场上刚了近1h，没搞出来，发现自己这个憨憨把两个空格子没有共同点看成没有共同边

当然我这么菜就算看对也不一定会做就是了，但yssy好做很多

若$m equiv 0(mod 3)$,则我们把$2,5,8,11,cdots,m-1$列全部变为空格子

若$m otequiv 0(mod 3)$,则我们把$1,4,7,10,cdots,(m or m-1)$列全部变为空格子

然后两个相邻的空列要记得连起来

CF1450C2

CF(gym102900B)

[CF1364D]Ehab's Last Corollary

jly答辩的时候，我完全没意识到自己居然做过，还是学弟提醒我我才知道我居然做过

#include <bits/stdc++.h>
 
#define Mod 998244353
 
using namespace std;
 
 
typedef long long ll;
 
inline int read() {
    int out = 0;
    bool flag = false;
    register char cc = getchar();
    while (cc < '0' || cc > '9') {
        if (cc == '-') flag = true;
        cc = getchar();
    }
    while (cc >= '0' && cc <= '9') {
        out = (out << 3) + (out << 1) + (cc ^ 48);
        cc = getchar();
    }
    return flag ? -out : out;
}
 
inline void write(int x) {
    if (x < 0) putchar('-'), x = -x;
    if (x == 0) putchar('0');
    else {
        int num = 0;
        char cc[20];
        while (x) cc[++num] = x % 10 + 48, x /= 10;
        while (num) putchar(cc[num--]);
    }
    putchar(' ');
}
 
ll ksm(ll x, ll y) {
    ll res = 1;
    while (y) {
        if (y & 1) res = res * x % Mod;
        x = x * x % Mod;
        y >>= 1;
    }
    return res;
}


int n, m, k, head[400010], to[400010], nxt[400010], cnt = -1;

void add(int u, int v) {
    to[++cnt] = v;
    nxt[cnt] = head[u];
    head[u] = cnt;
} 


int dep[400010], fa[400010], dfn[400010];

vector<int> ans, x, y;

void print() {
    if (ans.size() <= k) {
        puts("2");
        cout << ans.size() << endl;
        for (auto p : ans) write(p);
    }
    else {
        puts("1");
        for (int i = 0; i < (k + 1) / 2; i++) write(ans[i * 2]);
    }
}

void dfs(int u, int fae, int opt) {
    dep[u] = dep[fa[u]] + 1;
    dfn[dep[u]] = u;
    if (opt) x.push_back(u);
    else y.push_back(u);
    for (int i = head[u]; i != -1; i = nxt[i]) {
        if ((i ^ 1) == fae) continue;
        int v = to[i];
        if (dep[v]) {
            for (int j = dep[v]; j <= dep[u]; j++) ans.push_back(dfn[j]);
            print();
            exit(0);
        }
        fa[v] = u;
        dfs(v, i, opt ^ 1);
    }
}

int main() {
    n = read(), m = read(), k = read();
    memset(head, -1, sizeof(head));
    for (int i = 1; i <= m; i++) {
        int u = read(), v = read();
        add(u, v); add(v, u);
    }
    dfs(1, -1, 0);
    if (x.size() >= (k + 1) / 2) {
        puts("1");
        for (int i = 0; i < (k + 1) / 2; i++) write(x[i]);
    }
    else {
        puts("1");
        for (int i = 0; i < (k + 1) / 2; i++) write(y[i]);
    }
    return 0;
}

「IOI2019」景点划分

#include <bits/stdc++.h>

using namespace std;

const int N = 1e5 + 10, M = 2e5 + 10;

int n, m, a, b, c, A = 1, B = 2, C = 3;

int head[N], to[M << 1], nxt[M << 1], cnt;

void add_edge(int u, int v) {
    to[++cnt] = v, nxt[cnt] = head[u], head[u] = cnt;
}

vector<int> son[N]; bool vis[N]; int fa[N];

void dfs(int u) {
    vis[u] = true;
    for (int i = head[u]; i; i = nxt[i]) {
        int v = to[i];
        if (vis[v]) continue;
        dfs(v), son[u].push_back(v), fa[v] = u;
    }
}

int sze[N], g, ans[N];

void find(int u) {
    bool flag = true;
    sze[u] = 1;
    for (int i = son[u].size() - 1; i >= 0; i--) {
        int v = son[u][i];
        find(v), sze[u] += sze[v];
        if (sze[v] > (n / 2)) flag = false;
    }
    if (n - sze[u] > (n / 2)) flag = false;
    if (flag) g = u;
}

int t[N];

void sign(int u, int p) {
    t[u] = p;
    for (int i = son[u].size() - 1; i >= 0; i--) {
        int v = son[u][i];
        sign(v, p);
    }
}

bool pd(int u) {
    for (int i = head[u]; i; i = nxt[i]) {
        if (!t[to[i]]) return true;
    }
    for (int i = son[u].size() - 1; i >= 0; i--) {
        int v = son[u][i];
        if (pd(v)) return true;
    }
    return false;
}

void go(int u, int p, int q) {
    if (ans[u] || t[u] != q) return ;
    if (p == A) ans[u] = (a > 0 ? A : -1), a--;
    if (p == B) ans[u] = (b > 0 ? B : -1), b--;
    for (int i = head[u]; i; i = nxt[i]) {
        int v = to[i];
        go(v, p, q);
    }
}

int main() {
    scanf("%d%d", &n, &m);
    scanf("%d%d%d", &a, &b, &c);
    if (a > b) swap(a, b), swap(A, B);
    if (a > c) swap(a, c), swap(A, C);
    if (b > c) swap(b, c), swap(B, C);
    for (int i = 1; i <= m; i++) {
        int u, v; scanf("%d%d", &u, &v); u++, v++;
        add_edge(u, v), add_edge(v, u);
    }
    dfs(1), find(1);
    for (int i = son[g].size() - 1; i >= 0; i--) {
        int v = son[g][i];
        if (sze[v] >= a) {
            sign(v, 1), go(v, A, 1), go(g, B, 0);
            for (int j = 1; j <= n; j++) {
                if (ans[j] > 0) printf("%d ", ans[j]);
                else printf("%d ", C);
            }
            return 0;
        }
    }
    int s = n - sze[g];
    //cout << s << endl;
    sign(g, 1);
    for (int i = son[g].size() - 1; i >= 0 && s < a; i--) {
        int v = son[g][i]; //cout << sze[v] << " ";
        if (!pd(v)) continue;
        sign(v, 0), s += sze[v];
    }
    if (s < a) {
        //cout << s << " " << a << endl;
        for (int i = 1; i <= n; i++) printf("0 ");
        putchar('
');
        return 0;
    }
    go(fa[g], A, 0), go(g, B, 1);
    for (int i = 1; i <= n; i++) {
        if (ans[i] > 0) printf("%d ", ans[i]);
        else printf("%d ", C);
    }
    return 0;
}

CF(gym101221A)

CF1470D

移球游戏