Codeforces Round #364 (Div. 1) (差一个后缀自动机)

B. Connecting Universities

大意: 给定树, 给定2*k个点, 求将2*k个点两两匹配, 每个匹配的贡献为两点的距离, 求贡献最大值

单独考虑每条边$(u,v)$的贡献即可, 最大贡献显然是左右两侧点的最小值.

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <math.h>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <string.h>
#include <bitset>
#define REP(i,a,n) for(int i=a;i<=n;++i)
#define PER(i,a,n) for(int i=n;i>=a;--i)
#define hr putchar(10)
#define pb push_back
#define lc (o<<1)
#define rc (lc|1)
#define mid ((l+r)>>1)
#define ls lc,l,mid
#define rs rc,mid+1,r
#define x first
#define y second
#define io std::ios::sync_with_stdio(false)
#define endl '\n'
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int P = 1e9+7, INF = 0x3f3f3f3f;
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}
ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}
//headconst int N = 1e6+10;
int n, k;
int a[N], sz[N];
vector<int> g[N];
ll ans;void dfs(int x, int fa) {sz[x] = a[x];for (int y:g[x]) if (y!=fa) { dfs(y,x), sz[x]+=sz[y];ans += min(sz[y], k-sz[y]);}
}int main() {scanf("%d%d", &n, &k),k*=2;REP(i,1,k) { int t;scanf("%d", &t);a[t] = 1;}REP(i,2,n) {int u, v;scanf("%d%d", &u, &v);g[u].pb(v),g[v].pb(u);}dfs(1,0);printf("%lld\n", ans);
}

C. Break Up

大意: 无向有权图有重边自环, 求删除两条边使得s与t不连通, 且两条边的边权和最小.

先求出任意一条最短路径, 边数显然不超过$n$, 暴力枚举这$n$条边然后再tarjan即可, 复杂度O(n(m+n))

算是挺简单的了, 还是打了好久, 一直卡在怎么判断删除一条边后是否连通, 后来发现tarjan后从s->t经过的桥一定是一条链, 所以直接dfs就好了, 最后还要注意边权1e9+1e9爆掉0x3f3f3f3f了.

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <math.h>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <string.h>
#include <bitset>
#define REP(i,a,n) for(int i=a;i<=n;++i)
#define PER(i,a,n) for(int i=n;i>=a;--i)
#define hr putchar(10)
#define pb push_back
#define lc (o<<1)
#define rc (lc|1)
#define mid ((l+r)>>1)
#define ls lc,l,mid
#define rs rc,mid+1,r
#define x first
#define y second
#define io std::ios::sync_with_stdio(false)
#define endl '\n'
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int P = 1e9+7, INF = ~0u>>1;
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}
ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}
//headconst int N = 3e4+10;
int n, m, S, T;
int w[N];
struct _ {int to,id;} fa[N];
vector<_> g[N];
int dfn[N], low[N], isbridge[N], clk;
void tarjan(int x, int fa, int z) {dfn[x]=low[x]=++clk;for (auto &&e:g[x]) if (e.id!=z) {int y = e.to, id = e.id;if (!dfn[y]) {tarjan(y,id,z);low[x]=min(low[x],low[y]);if (low[e.to]>dfn[x]) isbridge[id]=1;} else if (dfn[y]<dfn[x]&&id!=fa) { low[x]=min(low[x],dfn[y]);}}
}
int vis[N], c[N];
int dfs(int x) {if (x==T) return 1;for (auto e:g[x]) if (!vis[e.id]) {vis[e.id] = 1;if (dfs(e.to)) return c[e.id] = 1;}return 0;
}int main() {scanf("%d%d%d%d", &n, &m, &S, &T);REP(i,1,m) { int u, v;scanf("%d%d%d", &u, &v, w+i);g[u].pb({v,i}), g[v].pb({u,i});}queue<int> q;fa[S].to=-1, q.push(S);while (q.size()) {int x = q.front(); q.pop();for (auto &&e:g[x]) if (!fa[e.to].to) {fa[e.to]={x,e.id}, q.push(e.to);}}if (!fa[T].to) return puts("0\n0"),0;int ans = INF;vector<int> vec;for (int x=T; x!=S; x=fa[x].to) {int id = fa[x].id;memset(vis,0,sizeof vis);memset(c,0,sizeof c);vis[id] = 1;if (!dfs(S)) {if (ans>w[id]) ans = w[id],vec.clear(),vec.pb(id);continue;}memset(dfn,0,sizeof dfn);memset(isbridge,0,sizeof isbridge);clk = 0;tarjan(S,0,id);REP(i,1,m) if (c[i]&&isbridge[i]&&ans>w[id]+w[i]) {ans=w[id]+w[i];vec.clear();vec.pb(id), vec.pb(i);}}if (ans==INF) return puts("-1"),0;printf("%d\n%d\n", ans, int(vec.size()));for (int t:vec) printf("%d ", t); hr;
}

D. Huffman Coding on Segment

莫队一下, 然后将出现次数小于等于$\sqrt{n}$的暴力合, 其余的用堆合, 复杂度$O(m\sqrt{n}logn)$, 看了下最优解, 好像可以排序一下省去堆从而优化掉一个log

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <math.h>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <string.h>
#include <bitset>
#define REP(i,a,n) for(int i=a;i<=n;++i)
#define PER(i,a,n) for(int i=n;i>=a;--i)
#define hr putchar(10)
#define pb push_back
#define lc (o<<1)
#define rc (lc|1)
#define mid ((l+r)>>1)
#define ls lc,l,mid
#define rs rc,mid+1,r
#define x first
#define y second
#define io std::ios::sync_with_stdio(false)
#define endl '\n'
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int P = 1e9+7, INF = 0x3f3f3f3f;
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}
ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}
//head#ifdef ONLINE_JUDGE
const int N = 1e6+10;
#else
const int N = 111;
#endifint n, m, sqn;
int blo[N], cnt[N], sum[N], s[N], a[N];
struct _ {int l,r,id;bool operator < (const _ & rhs) const {return blo[l]^blo[rhs.l]?l<rhs.l:blo[l]&1?r<rhs.r:r>rhs.r;}
} e[N];
ll ans[N];
vector<int> q;void upd(int x, int d) {--sum[cnt[x]];cnt[x]+=d;++sum[cnt[x]];
}ll calc() {ll ans = 0;REP(i,1,sqn) s[i] = sum[i];priority_queue<int,vector<int>,greater<int> > Q;int pre = 0;REP(i,1,sqn) if (s[i]) {if (pre) {int x = pre+i;ans += x;if (x>sqn) Q.push(x);else ++s[x];--s[i], pre = 0;}if (s[i]&1) --s[i], pre = i;ans += s[i]*i;if (i*2<=sqn) s[i*2]+=s[i]/2;else {REP(j,1,s[i]/2) Q.push(i*2);}}if (pre) Q.push(pre);for (auto i:q) if (cnt[i]>sqn) Q.push(cnt[i]);while (Q.size()>1) {int x = Q.top(); Q.pop();x += Q.top(); Q.pop();ans += x, Q.push(x);}return ans;
}int main() {scanf("%d", &n), sqn = sqrt(n);REP(i,1,n) scanf("%d",a+i),++cnt[a[i]],blo[i]=i/sqn;REP(i,1,N-1) if (cnt[i]>sqn) q.pb(i);memset(cnt,0,sizeof cnt);scanf("%d", &m);REP(i,1,m) scanf("%d%d",&e[i].l,&e[i].r),e[i].id=i;sort(e+1,e+1+m);int ql=1,qr=0;REP(i,1,m) {while (ql<e[i].l) upd(a[ql++],-1);while (qr>e[i].r) upd(a[qr--],-1);while (ql>e[i].l) upd(a[--ql],1);while (qr<e[i].r) upd(a[++qr],1);ans[e[i].id]=calc();}REP(i,1,m) printf("%lld\n", ans[i]);
}

E. Cool Slogans

后缀自动机还没学, 以后补了