Finding nth prime number (large number) (Optimization)

This was something handy I learned. Actually the problem is pretty easy, but when finding the nth prime where n>1000000 it takes way to long in the conventional way youre thinking. Here is an optimized solution to it, that reduces the time complexity. If you have any doubts, ask!

I think you can even optimize it further by doing p=p+2 and num=num+2. Try it out and see

def prime(chk):
if(chk%2==0):
return False
else:
p=3
while(p<chk**0.5+1):
if(chk%p==0):
return False
p=p+1
return True



def is_prime(x):
count=2
num=4
while(count<x):
if prime(num):
count+=1
num1=num
num=num+1
return num1

result=is_prime("Enter the nth term here")
print result

Program to print out the letters present in one word and absent in the other.

If you have any doubts, please do ask.

#include<stdio.h>
main()
{
    int i,j,flag=0;
char name1[10],name2[10];
scanf("%s",name1);
scanf("%s",name2);
for(i=0;i<strlen(name2);i++)
{
for(j=0;j<strlen(name1);j++)
{
if(name2[i]==name1[j])
flag=1;
}
if(flag==0)
{printf("%c",name2[i]);

}
else
    flag=0;
}}

Program to print out numbers separated by stars with the occurrence defined by the number printed.

This will print out something like this
1
2*2
3*3*3
4*4*4*4
and then the reverse image.
If you have any doubt, please do ask.

#include<stdio.h>
main()
{
int i=1,j=2,z=4,k;
printf("%d\n",i);
for(k=0;k<3;k++)
{
for(i=2;i<z-1;i++)
{
printf("%d*",j);
}
printf("%d\n");
j++;
z++;
}
j=4;
for(k=0;k<3;k++)
{
for(i=2;i<z-2;i++)
{
printf("%d*",j);
}
printf("%d\n");
j--;
z--;
}
printf("%d",1);
}

String reversal without string.h

This is a program to reverse a string without the string.h header. If you have any doubts, please do ask.

#include<stdio.h>
main()
{
int i,count=0,j=0;
char string[10],final[10];
scanf("%s",string);
for(i=0;string[i]!='\0';i++)
count++;
count--;
for(i=count;i>=0;i--)
{
final[j]=string[i];
j++;
}
final[j]='\0';
printf("%s",final);
}

Program for quick sort

Program to implement quick sort. If you need help, comment below

#include<stdio.h> int a[20],b[20],n,z; void quick(int x[],int first,int last) { int pivot; if(first<last) { pivot=partition(x,first,last); quick(x,first,pivot-1); quick(x,pivot+1,last); } } int partition(int x[],int first,int last) { int pivot,temp,i,j; pivot=first; i=first; j=last; while(i<j) { while((x[i]<=x[pivot])&&(i<last)) i++; while(x[j]>x[pivot]) j--; if(i<j) { temp=x[i]; x[i]=x[j]; x[j]=temp; } for(z=1;z<=n;z++) printf("%d\t ",a[z]); printf("\n"); } temp=x[pivot]; x[pivot]=x[j]; x[j]=temp; return j; } int main() { int i,j,c,ch; printf("\nQuicksort"); printf("\nEnter the no. of elements in the array:\t"); scanf("%d",&n); printf("\nEnter the elements into the array:\n"); for(i=1;i<=n;i++) scanf("%d",&a[i]); quick(a,1,n); printf("\nAfter sorting:\n"); for(i=1;i<=n;i++) printf("%d ",a[i]); }

Program for merge sort.

Program for merge sort. If you need help, feel free to ask.

#include<stdio.h> void mergesort(int x[20],int n) { int temp[20],i,j,k,l1,l2,size,u1,u2,a; size=1; while(size<n) { l1=0; k=0; while(l1+size<n) { l2=l1+size; u1=l2-1; u2=((l2+size-1<n)?l2+size-1:n-1); for(i=l1,j=l2;i<=u1&&j<=u2;k++) { if(x[i]<=x[j]) { temp[k]=x[i]; i++; } else { temp[k]=x[j]; j++; } } for(;i<=u1;k++) { temp[k]=x[i]; i++; } for(;j<=u2;k++) { temp[k]=x[j]; j++; } l1=u2+1; } for(i=l1;k<n;k++) temp[k++]=x[i]; for(i=0;i<n;i++) x[i]=temp[i]; size=size*2; printf("\n"); for(a=0;a<n;a++) printf("%d ",x[a]); printf("\n"); } } main() { int x[20],n,i; printf("\nEnter the value of the number of elements you wish to enter\n"); scanf("%d",&n); printf("\nEnter values of the elements you wish to sort"); for(i=0;i<n;i++) scanf("%d",&x[i]); printf("\nBefore Sorting this is how it looks\n:"); for(i=0;i<n;i++) printf(" %d",x[i]); mergesort(x,n); }

Program for heap sort

Program for Heap Sort. Kinda tricky program. If you need help, comment below

#include<stdio.h> int tree[20],n,ah[20],c=0; void build(int m,int item) { int ptr,par,f=0; m=m+1; ptr=m; while(ptr>1) { par=ptr/2; if(item<=tree[par]) { tree[ptr]=item; f=1; break; } tree[ptr]=tree[par]; ptr=par; } if(f==0) tree[1]=item; } void delheap(int k,int m) { int left,right,ptr,last,i; ah[k]=tree[1]; last=tree[m]; m=m-1; ptr=1; left=2; right=3; while(right<=m) { if((last>=tree[left])&&(last>=tree[right])) { tree[ptr]=last; return; } if(tree[right]<=tree[left]) { tree[ptr]=tree[left]; ptr=left; } else { tree[ptr]=tree[right]; ptr=right; } left=2*ptr; right=left+1; } if((left==m)&&(last<tree[left])) { tree[ptr]=tree[left]; ptr=left; } tree[ptr]=last; c++; printf("\n\nPass %d: ",c); for(i=1;i<=m;i++) printf("%d ",tree[i]); } main() { int i,j; printf("\nEnter total number of elements:"); scanf("%d",&n); printf("\nEnter elements to be inserted : "); for(i=1;i<=n;i++) scanf("%d",&tree[i]); for(i=1;i<n;i++) build(i,tree[i+1]); printf("\n\nHeap : "); for(i=1;i<=n;i++) printf("%d ",tree[i]); for(i=n,j=1;i>1;i--,j++) delheap(j,i); if(i==1) ah[n]=tree[1]; printf("\n\nHeap sort : "); for(i=1;i<=n;i++) printf("%d ",ah[i]); }

Program to count number of occurrences of a word in a sentence.

Simple C program to count the number of occurrences of a word in a sentence. If you need help, feel free to ask.

#include<stdio.h>
#include<string.h>
main()
{
  int len,c=0,i=0,j=0,ans=0;
  char str1[50],str2[20],new[20];
  printf("\n enter the text: ");
  gets(str1);
  printf("\n enter the word: ");
  gets(str2);
  len=strlen(str1);
  for(i=0;i<=len;i++)
   {
     if(str1[i]!=' ')
      {
       new[j]=str1[i];
       j++;
      }
     if(str1[i]==' '||str1[i]=='\0')
       {
           new[j]='\0';
           j=0;
           ans=strcmp(new,str2);
           if(ans==0)
             c++;
        }
    }
   printf("\n the number of occurence is %d\n",c);
}

Largest and second largest of all rows and columns of a matrix.

This is a C program to find the largest and second largest element of all the rows and columns of a matrix. If you have any doubts, please feel free in asking.

#include<stdio.h>

main()

{

 int a[50][50],size,n,m,i,j,large,slarge;

 printf("enter size of matrix(row and column):");

 scanf("%d %d",&n,&m);

 printf("\n enter the elements:");

 for(i=0;i<n;i++)

 {

  for(j=0;j<m;j++)

   scanf("%d",&a[i][j]);

 }

 printf("\n the inputed matrix is:\n");

 for(i=0;i<n;i++)

  {

   for(j=0;j<m;j++)

    printf("\t%d  ",a[i][j]);

   printf("\n");

  }

 for(i=0;i<n;i++)

  {

    slarge=a[i][0];

    large=a[i][0];

    for(j=0;j<m;j++)

     {

       if(large<a[i][j])

         large=a[i][j];

     }

    printf("\n the largest of row%d is %d",i+1,large);

    for(j=0;j<m;j++)

     {

       if(a[i][j]!=large)

       {

        if(slarge<a[i][j])

          slarge=a[i][j];

       }

     }

    printf("\nthe seceond largest of row%d is %d",i+1,slarge);

   }

 for(j=0;j<m;j++)

  {

    slarge=a[0][j];

    large=a[0][j];

   

for(i=0;i<n;i++)

    {

      if(large<a[i][j])

        large=a[i][j];

    }

    printf("\n the largest of column %dis %d",j+1,large);

    for(i=0;i<n;i++)

     {

       if(a[i][j]!=large)

        {

          if(slarge<a[i][j])

            slarge=a[i][j];

        }

     }

    printf("\nthe second largest of column %dis %d\n",j+1,slarge);

  }

 }