#### Problem :

Given an array of integers, you need to segregate odd and even numbers in an array.

Please note : Order of elements can be changed.

**For example:**

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arr[] = {12, 17, 70, 15, 22, 65, 21, 90} Array after separating odd and even numbers : {12, 90, 70, 22, 15, 65, 21, 17} |

#### Algorithm:

Lets say array is arr[]

- Initialise two index variable , left=0 and right=arr.length-1
- Increment left variable until you get odd number
- Decrement right variable until you get even number.
- If left < right, swap arr[left] and arr[right]
- In the end, you will see that you have even numbers on left side and odd numbers on right side.

### Java code to separate odd and even numbers in an array :

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package org.arpit.java2blog; public class SeparateOddEvenMain { public static void main(String[] args) { int arr[]={12, 17, 70, 15, 22, 65, 21, 90}; System.out.println("Original Array: "); for (int i = 0; i < arr.length; i++) { System.out.print(arr[i]+" "); } arr=separateEvenOddNumbers(arr); System.out.println("nArray after separating even and odd numbers : "); for (int i = 0; i < arr.length; i++) { System.out.print(arr[i]+" "); } } public static int[] separateEvenOddNumbers(int arr[]) { int left=0; int right=arr.length-1; for (int i = 0; i < arr.length; i++) { while(arr[left]%2==0) { left++; } while(arr[right]%2==1) { right--; } if(left<right) { int temp=arr[left]; arr[left]=arr[right]; arr[right]=temp; } } return arr; } } |

when you run above program, you will get below output:

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Original Array: 12 17 70 15 22 65 21 90 Array after separating even and odd numbers : 12 90 70 22 15 65 21 17 |

Thanks. Very helpful but how can we merge two unsorted arrays and also find smaller number of that unsorted array

Below is better approach :

while(low<=high){

if(arr[low]%2!=0){

if(arr[high]%2==0) {

int temp = arr[low];

arr[low] = arr[high];

arr[high] = temp;

low++;

high–;

}else{

high–;

}

}else{

low++;

}

}