codeforce 919

A：题链

#include<bits/stdc++.h>
using namespace std;
int n,m,a,b;
long double ans;
int main () {
    scanf("%d %d",&n,&m);
    ans=1e9;
    for(int i=1;i<=n;i++) {
        scanf("%d %d",&a,&b);
        ans=min(ans,(long double)1.0*a/b);
    }
    printf("%.9Lf",ans*m);
}

B:题链 打表

#include <bits/stdc++.h>
using namespace std;
#define inf 1e10
//#define getchar nc
//#define min(a,b) ((a)<(b)?(a):(b))
//#define max(a,b) ((a)>(b)?(a):(b))
#define sight(c) ('0'<=c&&c<='9')
//#define swap(a,b) a^=b,b^=a,a^=b
#define LL long long
#define deg printf
#define dput put
#define dputc putchar
#define db double 
#define eho(x) for(int i=head[x];i;i=net[i])
int xx;
inline char nc(){
static char buf[1000000],*p1=buf,*p2=buf;
return p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++;
}
inline void read(int &x){
    static char c;
    for (c=getchar();!sight(c);c=getchar());
    for (x=0;sight(c);c=getchar())x=x*10+c-48;
}
set<LL> S; 
vector<LL> V;
void dfs(LL x, int y) {
    if (x > inf) return;
    if (!y) S.insert(x);
    for (int i=1;i<=min(9,y);i++)
    dfs(x * 10 + i, y - i);
    if (x) dfs(x * 10, y);
}
int main(void) {
    dfs(0, 10); read(xx);
    for (auto x : S) V.push_back(x);
    printf("%lld\n", V[xx - 1]);
    return 0;
}

C：题链 

记得特判1

#include <bits/stdc++.h>
using namespace std;
//#define getchar nc
//#define min(a,b) ((a)<(b)?(a):(b))
//#define max(a,b) ((a)>(b)?(a):(b))
#define sight(c) ('0'<=c&&c<='9')
//#define swap(a,b) a^=b,b^=a,a^=b
#define LL long long
#define deg printf
#define dput put
#define dputc putchar
#define db double 
#define eho(x) for(int i=head[x];i;i=net[i])
inline char nc(){
static char buf[1000000],*p1=buf,*p2=buf;
return p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++;
}
inline void read(LL &x){
    static char c;
    for (c=getchar();!sight(c);c=getchar());
    for (x=0;sight(c);c=getchar())x=x*10+c-48;
}
inline void read(int &x){
    static char c;
    for (c=getchar();!sight(c);c=getchar());
    for (x=0;sight(c);c=getchar())x=x*10+c-48;
}
int n, m, k, ans, a[2005][2005], b[2005][2005], c[2005][2005];
char s[2005][2005];
bool rr1(int x, int y) {
    return y+k-1>m?0:b[x][y + k - 1] - b[x][y - 1] == k;
}
bool rr2(int x, int y) {
    return x+k-1>n?0:c[x + k - 1][y] - c[x - 1][y] == k;}
int main() {
    read(n);read(m);read(k);
    for(int i=1;i<=n;i++) scanf("%s", s[i] + 1);
    for (int i=1;i<=n;i++)for (int j=1;j<=m;j++) 
        a[i][j]=s[i][j]=='.'?1:0;
    for(int i=1;i<=n;i++) for (int j=1;j<=m;j++)
    b[i][j] = b[i][j - 1] + a[i][j];
    for(int i=1;i<=n;i++) for (int j=1;j<=m;j++)
    c[i][j] = c[i - 1][j] + a[i][j];
    for(int i=1;i<=n;i++) for (int j=1;j<=m;j++)
    if (rr1(i, j)) ans++;
    if (k^1) {for (int i=1;i<=n;i++)for(int j=1;j<=m;j++) if (rr2(i, j)) ans++;}
    printf("%d\n", ans);
    return 0;
}

D:题链

做dp即可

//#pragma GCC optimize("-O2")
#include<bits/stdc++.h>
#define LL long long
#define deg printf
#define sight(c) ('0'<=c&&c<='9')
#define N 600007
#define dput put
#define dputc putchar
#define db double 
#define eho(x) for(int i=head[x];i;i=net[i])
int in[N],x,y,tot,head[N],net[N],fall[N],n,m,f[N][26],ans,a[N],tog;
char ch[N];
using namespace std;
queue<int> Q;
inline void add(int x,int y){
    fall[++tot]=y; net[tot]=head[x]; head[x]=tot;
}
inline void read(int &x){
    static char c;
    for (c=getchar();!sight(c);c=getchar());
    for (x=0;sight(c);c=getchar())x=x*10+c-48;
}
void write(int x){if (x<10) {putchar('0'+x); return;} write(x/10); putchar('0'+x%10);}
inline void writeln(int x){ if (x<0) putchar('-'),x*=-1; write(x); putchar('\n'); }
inline void writel(int x){ if (x<0) putchar('-'),x*=-1; write(x); putchar(' '); }
signed main() {
    read(n); read(m);
    scanf("%s",ch+1);
    while (m--) {
        read(x),read(y); add(x,y); in[y]++;
    }
    for (int i=1;i<=n;i++) 
     if (!in[i]) { Q.push(i); f[i][ch[i]-'a']=1;}
    while (!Q.empty()) {
        x=a[++tog]=Q.front(); Q.pop();
        eho(x) {
            in[fall[i]]--;
            if (!in[fall[i]]) Q.push(fall[i]);
        } 
    }
    if (tog!=n) {
        printf("-1\n"); return 0;
    }
    for (int i=1;i<=n;i++) {
        x=a[i]; 
        eho(x) {
            for (int j=0;j<26;j++) {
             f[fall[i]][j]=max(f[fall[i]][j],f[x][j]+(ch[fall[i]]-'a'==j));
             if (f[fall[i]][j]>ans) ans=f[fall[i]][j];
            }
        }
        
    }
    printf("%d\n",ans);
    return 0;
}

E:题链

注意到p很小，那么对p暴力

#include <bits/stdc++.h>
using namespace std;
#define sight(c) ('0'<=c&&c<='9')
#define LL long long
#define deg printf
#define dput put
#define dputc putchar
#define db double 
#define eho(x) for(int i=head[x];i;i=net[i])
inline char nc(){
static char buf[1000000],*p1=buf,*p2=buf;
return p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++;
}
LL a, b, p, x, z, rrsb, rrsbrrsb, ans,c;
inline void read(LL &x){
    static char c;
    for (c=getchar();!sight(c);c=getchar());
    for (x=0;sight(c);c=getchar())x=x*10+c-48;
}
inline LL qsm(LL x, LL y) {
    static LL anw;
    for (anw=1;y;y>>=1,x=x*x%p) if (y&1) anw=anw*x%p;
    return anw;
}
void write(LL x){if (x<10) {putchar('0'+x); return;} write(x/10); putchar('0'+x%10);}
inline void writeln(LL x){ if (x<0) putchar('-'),x*=-1; write(x); putchar('\n'); }
inline void writel(LL x){ if (x<0) putchar('-'),x*=-1; write(x); putchar(' '); }
inline void Mo(LL &x){
    if (x<0) x=x%p+p; if (x>=p) x%=p; 
}
void gg(int i) {
     rrsb-=i; Mo(rrsb);
     rrsb*=qsm(p-1,p-2); Mo(rrsb);
}
void init() {
    read(a);read(b);read(p);read(x);
    z = 1;
    for(int i=1;i<p;i++) {
        z=z*a%p;
        rrsb=qsm(z,p-2)*b%p;
        gg(i);
        rrsbrrsb=(p-1)*rrsb+i;
        if (rrsbrrsb>x) continue;
        ans+=(x-rrsbrrsb)/(p*(p-1))+1;
    }
}
int main() {
    init();
    writeln(ans);
    return 0;
}