View source for Moving Negative Numbers to the Beginning of Array ← Moving Negative Numbers to the Beginning of Array

Makes positive numbers appear after the negative numbers in an array.

Complexity <math>\theta(n)</math>

No. of swaps in the worst case = <math> \lfloor n/2 \rfloor</math>

<syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

       int i, n, pi, ni, count = 0;
       int a[1000];
       printf("Enter size of array: ");
       scanf("%d",&n);
       printf("Enter numbers of array\n");
       for(i=0; i<n; i++)
       {
               scanf("%d",&a[i]);
       }
       ni = n-1;
       while(a[ni] >= 0)
               ni--;
       pi = 0;
       while(a[pi] < 0)
               pi++;
       while(ni > pi)
       {
               int temp = a[pi];
               a[pi] = a[ni];
               a[ni] = temp;
               while(a[ni] >= 0)
                       ni--;
               while(a[pi] < 0)
                       pi++;

       }

       for(i=0; i<n; i++)
       {
               printf("%d ", a[i]);
       }

} </syntaxhighlight>

Solution[edit]

We are scanning the array from two ends. We scan for positive numbers from left and negative numbers from right and swaps them. As soon as one of them finishes, the algorithm stops. There are n elements, so there can't be more than n/2 positive numbers or n/2 negative numbers.