我居然每道题都能想出来
虽然不是每道题都能写对，debug了很久/facepalm
C - Many Medians
排序后前N/2个数的中位数时排序后第N/2 + 1的数
其余的中位数都是排序后第N / 2的数
#include <iostream>
#include <cstdio>
#include <vector>
#include <set>
#include <cstring>
#include <string>
#include <ctime>
#include <algorithm>
#include <map>
#define MAXN 200005
#define pii pair<int,int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ba 823
#define mo 974711
//#define ivorysi
using namespace std;
typedef long long int64;
typedef double db;
int N;
int id[MAXN],X[MAXN],B[MAXN];
bool cmp(int a,int b) {
return X[a] < X[b];
}
int main() {
#ifdef ivorysi
freopen("f1.in","r",stdin);
#endif
scanf("%d",&N);
for(int i = 1 ; i <= N ; ++i) {
scanf("%d",&X[i]);
id[i] = i;
}
sort(id + 1,id + N + 1,cmp);
int T = N / 2;
for(int i = 1 ; i <= T ; ++i) {
B[id[i]] = X[id[T + 1]];
}
for(int i = T + 1 ; i <= N ; ++i) {
B[id[i]] = X[id[T]];
}
for(int i = 1 ; i <= N ; ++i) {
printf("%d
",B[i]);
}
return 0;
}
D - Binomial Coefficients
N取最大的，R取最接近N/2的
#include <iostream>
#include <cstdio>
#include <vector>
#include <set>
#include <cstring>
#include <ctime>
#include <map>
#include <algorithm>
#include <cmath>
#define MAXN 200005
#define pii pair<int,int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ba 823
#define mo 974711
//#define ivorysi
using namespace std;
typedef long long int64;
typedef double db;
int N,A[100005];
int main() {
#ifdef ivorysi
freopen("f1.in","r",stdin);
#endif
ios::sync_with_stdio(false);
scanf("%d",&N);
for(int i = 1 ; i <= N ; ++i) scanf("%d",&A[i]);
sort(A + 1,A + N + 1);
printf("%d ",A[N]);
double T = A[N] / 2.0;
int t = 1;
for(int i = 2 ; i <= N ; ++i) {
if(fabs(A[i] - T) < fabs(A[t] - T)) t = i;
}
printf("%d
",A[t]);
return 0;
}
E - Symmetric Grid
事实上我想的优化不用也是个奇快无比的搜索
复杂度是啥不知道，反正1ms
发现两行能匹配上一定是两行的字符集是相同的
两列能匹配上一定是两列的字符集相同
我们枚举某行作为第一行，然后找它字符集相同的一行作为最后一行，枚举匹配，然后每一列都固定了，最后给剩下的N - 2行找匹配就行
匹配条件是某一行正着读等于另一行反着读
特判奇数行奇数列和H = 1，W = 1
#include <iostream>
#include <cstdio>
#include <vector>
#include <set>
#include <cstring>
#include <ctime>
#include <map>
#include <algorithm>
#include <cmath>
#define MAXN 200005
#define pii pair<int,int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ba 823
#define ha 99994711
//#define ivorysi
using namespace std;
typedef long long int64;
typedef double db;
int H,W,St;
int Row[14][26],Col[14][26];
int matR[14][14],matC[14][14],idC[14],idR[14],mat[14];
bool vis[14],used[14];
char S[14][14];
void swapRow(int x,int y) {
if(x == y) return;
swap(idR[x],idR[y]);
for(int i = 1 ; i <= W ; ++i) swap(S[x][i],S[y][i]);
}
void swapCol(int x,int y) {
if(x == y) return;
swap(idC[x],idC[y]);
for(int i = 1 ; i <= H ; ++i) swap(S[i][x],S[i][y]);
}
bool match(int c) {
if(c == 0) {
memset(mat,0,sizeof(mat));
int cnt = 0;
for(int i = 2 ; i <= H - 1; ++i) {
if(mat[i]) continue;
for(int j = i + 1 ; j <= H - 1; ++j) {
if(mat[j]) continue;
bool f = 1;
for(int k = 1 ; k <= W ; ++k) {
if(S[i][k] != S[j][W - k + 1]) {
f = 0;
break;
}
}
if(f) {mat[i] = j;mat[j] = i;break;}
}
if(!mat[i] && cnt < 1 && (H & 1)) {
++cnt;
for(int k = 1 ; k <= W ; ++k) {
if(S[i][k] != S[i][W - k + 1]) return 0;
}
mat[i] = i;
}
else if(!mat[i]) return 0;
}
return 1;
}
if(c == W - c + 1) {
for(int i = 1 ; i <= W ; ++i) {
if(vis[i]) continue;
if(S[1][i] == S[H][i]) {
swapCol(i,c);
vis[c] = 1;
if(match(c - 1)) return 1;
vis[c] = 0;
swapCol(i,c);
}
}
}
else {
for(int i = 1; i <= W; ++i) {
if(vis[i]) continue;
if(matC[idC[c]][idC[i]]) {
if(S[1][c] == S[H][i] && S[1][i] == S[H][c]) {
vis[c] = vis[W - c + 1] = 1;
swapCol(i,W - c + 1);
if(match(c - 1)) return 1;
swapCol(i,W - c + 1);
vis[c] = vis[W - c + 1] = 0;
}
}
}
}
return 0;
}
bool check() {
for(int i = 2 ; i <= H ; ++i) {
if(matR[idR[1]][idR[i]]) {
if(used[idR[i]]) continue;
swapRow(i,H);
if(match((W & 1) ? W / 2 + 1 : W / 2)) return 1;
swapRow(i,H);
}
}
return 0;
}
void Solve() {
scanf("%d%d",&H,&W);
for(int i = 1 ; i <= H ; ++i) scanf("%s",S[i] + 1);
for(int i = 1 ; i <= H ; ++i) {
for(int j = 1 ; j <= W ; ++j) {
Row[i][S[i][j] - 'a']++;
}
}
for(int j = 1 ; j <= W ; ++j) {
for(int i = 1 ; i <= H ; ++i) {
Col[j][S[i][j] - 'a']++;
}
}
if(H == 1) {
int cnt = 0;
for(int i = 0 ; i <= 25 ; ++i) {
if(Row[1][i] & 1) ++cnt;
}
if(cnt > 1) puts("NO");
else puts("YES");
return;
}
else if(W == 1) {
int cnt = 0;
for(int i = 0 ; i <= 25 ; ++i) {
if(Col[1][i] & 1) ++cnt;
}
if(cnt > 1) puts("NO");
else puts("YES");
return;
}
for(int i = 1 ; i <= H ; ++i) {
for(int j = i ; j <= H ; ++j) {
bool f = 1;
for(int k = 0 ; k <= 25 ; ++k) {
if(Row[i][k] != Row[j][k]) {f = 0;break;}
}
matR[i][j] = matR[j][i] = f;
}
}
for(int i = 1 ; i <= W ; ++i) {
for(int j = i ; j <= W ; ++j) {
bool f = 1;
for(int k = 0 ; k <= 25 ; ++k) {
if(Col[i][k] != Col[j][k]) {f = 0;break;}
}
matC[i][j] = matC[j][i] = f;
}
}
for(int i = 1 ; i <= H ; ++i) idR[i] = i;
for(int i = 1 ; i <= W ; ++i) idC[i] = i;
for(int i = 1 ; i <= H ; ++i) {
used[i] = 1;
swapRow(i,1);
if(check()) {puts("YES");return;}
swapRow(i,1);
}
puts("NO");
}
int main() {
#ifdef ivorysi
freopen("f1.in","r",stdin);
#endif
Solve();
return 0;
}
F - Permutation Tree
合法的只有一条链上长叶子
把叶子删掉，搜出一条链，链的两端如果有叶子就长出来
然后用一个数组记录链上每个点长的叶子的个数
然后从左右开始比较，如果左边小于右边就跳出，如果右边小于左边就翻转后跳出
构造的时候一个长了k个叶子的点排序就是 p + 1,p + 2...p + k, p
代码能力不行，跪了三次QAQ
#include <iostream>
#include <cstdio>
#include <vector>
#include <set>
#include <cstring>
#include <ctime>
#include <map>
#include <algorithm>
#include <cmath>
#define MAXN 100005
#define pii pair<int,int>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ba 823
#define ha 99994711
//#define ivorysi
using namespace std;
typedef long long int64;
typedef double db;
int N;
struct node {
int to,next;
}E[MAXN * 2];
int sumE,head[MAXN],ind[MAXN],fa[MAXN],st,ed,D[MAXN];
int line[MAXN],tot;
void add(int u,int v) {
E[++sumE].to = v;
E[sumE].next = head[u];
head[u] = sumE;
}
void dfs(int u) {
ed = u;
for(int i = head[u] ; i ; i = E[i].next) {
int v = E[i].to;
if(v != fa[u] && ind[v] != -1) {
fa[v] = u;
dfs(v);
}
}
}
void Solve() {
scanf("%d",&N);
int u,v;
for(int i = 1 ; i < N ; ++i) {
scanf("%d%d",&u,&v);
add(u,v);add(v,u);
ind[u]++;ind[v]++;
}
if(N == 2) {
puts("1 2");return;
}
memcpy(D,ind,sizeof(ind));
for(int i = 1 ; i <= N ; ++i) {
if(ind[i] == 1) {
for(int j = head[i] ; j ; j = E[j].next) {
int v = E[j].to;
D[v]--;
}
D[i] = -1;
}
}
memcpy(ind,D,sizeof(ind));
for(int i = 1 ; i <= N ; ++i) {
if(ind[i] > 2) {puts("-1");return;}
}
for(int i = 1 ; i <= N ; ++i) {
if(ind[i] == 1) {st = i;dfs(st);break;}
}
if(!st) {
for(int i = 1 ; i <= N ; ++i) {
if(ind[i] == 0) {st = i;dfs(st);break;}
}
}
for(int i = head[ed] ; i ; i = E[i].next) {
int v = E[i].to;
if(v != fa[ed]) {
fa[v] = ed;
ed = v;
break;
}
}
for(int i = head[st] ; i ; i = E[i].next) {
int v = E[i].to;
if(!fa[v]) {
fa[st] = v;
st = v;
break;
}
}
ind[ed] = ind[st] = 1;
int p = ed;
while(p) {
++tot;
for(int i = head[p] ; i ; i = E[i].next) {
int v = E[i].to;
if(ind[v] == -1) {
line[tot]++;
}
}
p = fa[p];
}
int L = 1,R = tot;
while(L <= tot && R >= 1) {
if(line[L] < line[R]) break;
else if(line[L] > line[R]) {reverse(line + 1,line + tot + 1);break;}
++L;--R;
}
p = 2;
printf("%d",1);
for(int i = 2 ; i <= tot ; ++i) {
for(int j = p + 1 ; j <= p + line[i] ; ++j) {
printf(" %d",j);
}
printf(" %d",p);
p = p + line[i] + 1;
}
putchar('
');
}
int main() {
#ifdef ivorysi
freopen("f1.in","r",stdin);
#endif
Solve();
return 0;
}