版权声明：https://blog.csdn.net/huashuimu2003 https://blog.csdn.net/huashuimu2003/article/details/87364606
A. BZOj 4390: [Usaco2015 dec]Max Flow
题目
题解
树上差分的模板题。
代码
#include<bits/stdc++.h>
using namespace std;
const int maxn=5e4+10;
template<typename T>inline void read(T &x)
{
x=0;
T f=1,ch=getchar();
while (!isdigit(ch)) ch=getchar();
if (ch=='-') f=-1, ch=getchar();
while (isdigit(ch)) x=(x<<1)+(x<<3)+(ch^48), ch=getchar();
x*=f;
}
int ver[maxn<<1],Next[maxn<<1],head[maxn],len;
inline void add(int x,int y)
{
ver[++len]=y,Next[len]=head[x],head[x]=len;
}
int fa[maxn],d[maxn],f[maxn][21];
inline void dfs1(int x,int father,int deep)
{
fa[x]=father,d[x]=deep;
for (int i=1;i<16;++i)
f[x][i]=f[f[x][i-1]][i-1];
for (int i=head[x];i;i=Next[i])
{
int y=ver[i];
if (y==father) continue;
f[y][0]=x;
dfs1(y,x,deep+1);
}
}
inline int lca(int x,int y)
{
if (d[x]>d[y]) swap(x,y);
for (int i=15;i>=0;--i)
if (d[f[y][i]]>=d[x])
y=f[y][i];
if (x==y) return x;
for (int i=15;i>=0;--i)
if (f[x][i]!=f[y][i])
x=f[x][i],y=f[y][i];
return f[x][0];
}
int siz[maxn],sum[maxn],ans;
inline void dfs2(int x,int father)
{
siz[x]=sum[x];
for (int i=head[x];i;i=Next[i])
{
int y=ver[i];
if (y==father) continue;
dfs2(y,x);
siz[x]+=siz[y];
}
ans=max(ans,siz[x]);
}
int main()
{
int n,k;
read(n);read(k);
for (int i=1;i<n;++i)
{
int x,y;
read(x);read(y);
add(x,y);add(y,x);
}
dfs1(1,0,1);
for (int i=1;i<=k;++i)
{
int a,b;
read(a);read(b);
int c=lca(a,b);
++sum[a],++sum[b],--sum[c];
if (c!=1) --sum[fa[c]];
}
dfs2(1,0);
printf("%d\n",ans);
return 0;
}
B. POJ 3417 Network
题目
题解
这道题借鉴了算法进阶的思路。
代码
#include<algorithm>
#include<bitset>
#include<cctype>
#include<cerrno>
#include<clocale>
#include<cmath>
#include<complex>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<deque>
#include<exception>
#include<fstream>
#include<functional>
#include<limits>
#include<list>
#include<map>
#include<iomanip>
#include<ios>
#include<iosfwd>
#include<iostream>
#include<istream>
#include<ostream>
#include<queue>
#include<set>
#include<sstream>
#include<stack>
#include<stdexcept>
#include<streambuf>
#include<string>
#include<utility>
#include<vector>
#include<cwchar>
#include<cwctype>
using namespace std;
const int maxn=1e5+10;
template<typename T>inline void read(T &x)
{
x=0;
T f=1,ch=getchar();
while (!isdigit(ch)) ch=getchar();
if (ch=='-') f=-1, ch=getchar();
while (isdigit(ch)) x=(x<<1)+(x<<3)+(ch^48), ch=getchar();
x*=f;
}
int ver[maxn<<1],Next[maxn<<1],head[maxn],len;
inline void add(int x,int y)
{
ver[++len]=y,Next[len]=head[x],head[x]=len;
}
int fa[maxn],d[maxn],f[maxn][21];
inline void dfs1(int x,int father,int deep)
{
fa[x]=father,d[x]=deep;
for (int i=1;i<=20;++i)
f[x][i]=f[f[x][i-1]][i-1];
for (int i=head[x];i;i=Next[i])
{
int y=ver[i];
if (y==father) continue;
f[y][0]=x;
dfs1(y,x,deep+1);
}
}
inline int lca(int x,int y)
{
if (d[x]>d[y]) swap(x,y);
for (int i=20;i>=0;--i)
if (d[f[y][i]]>=d[x])
y=f[y][i];
if (x==y) return x;
for (int i=20;i>=0;--i)
if (f[x][i]!=f[y][i])
x=f[x][i],y=f[y][i];
return f[x][0];
}
int siz[maxn],sum[maxn],ans;
inline void dfs2(int x,int father)
{
siz[x]=sum[x];
for (int i=head[x];i;i=Next[i])
{
int y=ver[i];
if (y==father) continue;
dfs2(y,x);
siz[x]+=siz[y];
}
}
int main()
{
int n,m;
read(n);read(m);
for (int i=1;i<n;++i)
{
int x,y;
read(x);read(y);
add(x,y);add(y,x);
}
dfs1(1,0,1);
for (int i=1;i<=m;++i)
{
int a,b;
read(a);read(b);
int c=lca(a,b);
++sum[a],++sum[b],sum[c]-=2;
}
dfs2(1,0);
for (int i=1;i<=n;++i)
if (!siz[i] && i!=1) ans+=m;
else if (siz[i]==1) ++ans;
printf("%d\n",ans);
return 0;
}
C. CF 739B Alyona and a tree
题目
代码
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=2e5+10;
template<typename T>inline void read(T &x)
{
x=0;
register int f=1;
register char ch=getchar();
while (!isdigit(ch)) { if (ch=='-') f=-1; ch=getchar();}
while (isdigit(ch)) x=(x<<1)+(x<<3)+(ch^48), ch=getchar();
x*=f;
}
template<typename T>inline void print(T x)
{
if (x<0) putchar('-'),x=-x;
if (x>9) print(x/10);
putchar(x%10+48);
}
int ver[maxn<<1],edge[maxn<<1],Next[maxn<<1],head[maxn],len;
inline void add(int x,int y,int z)
{
ver[++len]=y,edge[len]=z,Next[len]=head[x],head[x]=len;
}
ll d[maxn];//必须用long long，否则过不了，如果你想一直莫名WA的话，可以不管
int f[maxn][19];
int a[maxn];
int ans[maxn];
inline void dfs(int x,int fa,int dist)
{
d[x]=d[fa]+dist,f[x][0]=fa;
for (int i=1;i<=18;++i)
f[x][i]=f[f[x][i-1]][i-1];
for (int i=head[x];i;i=Next[i])
{
int y=ver[i],z=edge[i];
if (y==fa) continue;
dfs(y,x,z);
register int val=a[y],k=1,now=y;
while (k&&now)
{
if (d[now]-d[f[now][k]]<=val)
{
val-=d[now]-d[f[now][k]];
now=f[now][k];
k<<=1;
}
else k>>=1;
}
if (d[now]-d[f[now][0]]<=val)
now=f[now][0];
--ans[f[now][0]],++ans[f[y][0]];
}
ans[fa]+=ans[x];
}
int main()
{
int n,y,z;read(n);
for (int i=1;i<=n;++i)
read(a[i]);
for (int i=2;i<=n;++i)
{
read(y);read(z);
add(i,y,z);add(y,i,z);
}
dfs(1,0,0);
for (int i=1;i<=n;++i)
print(ans[i]),putchar(' ');
return 0;
}