9.3 | Study Notes

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First, the binary conversion

Output Hex: printf ( "% x", num);

Where x case hexadecimal output decision letter case

When a binary output to write a function that stores 0 and 1 with int arrays, but need special sentenced to zero, resulting in judgment forget WA

void bin(int n)
{
    if(n==0)cout<<'0';
    else{
    int a[100001];
    int cnt=0;
    while(n/2)
    {
        a[cnt++]=n%2;
        n/=2;
    }
    if(n%2)a[cnt++]=1;
    for(int i=cnt-1;i>=0;i--)cout<<a[i];}
}

 

Second, serpentine array

 

 

 

#include<bits/stdc++.h>
using namespace std;
int t,n,i,j;
int a[11][11];
void snake(int n)
{
    memset(a,0,sizeof(a));
    int i=1,j=1,cnt=1;
    while(cnt<(n*n))
    {
        while(j<n&&!a[i][j+1])a[i][j++]=(cnt++);
        while(i<n&&!a[i+1][j])a[i++][j]=(cnt++);
        while(j>1&&!a[i][j-1])a[i][j--]=(cnt++);
        while(i>1&&!a[i-1][j])a[i--][j]=(cnt++);
    }
    a[i][j]=n*n;
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=n;j++)cout<<a[i][j]<<' ';
        cout<<endl;
    }
}
int main()
{
    cin>>t;
    for(int i=0;i<t;i++)
    {
        cin>>n;
        cout<<"case #"<<i<<":\n";
        snake(n);
    }
    return 0;
}

 

(While loop inside the while loop may be changed for loop)

Key is a time to judge a vacancy is not the first time did not do it because they are written in judging a [i] [j], should actually be a [i + 1] [j] and the like

 

Three, n factorial the number of zeros in the tail (n <= 1000)

 

#include<bits/stdc++.h>
using namespace std;
int T,n,i;
int main()
{
    cin>>T;
    for(i=0;i<T;i++)
    {
        cin>>n;
        cout<<"case #"<<i<<":\n"<<n/5+n/25+n/125+n/625<<endl;
    }
    return 0;
}