Move Zeroes to end of Array in Java | LeetCode problem

Java code for Move All Zeroes to end of given Array without creating new Array with explanation

Problem Description :-

Given an integer array, move all 0's to the end of it while maintaining the relative order of the non-zero elements.

Note that you must do this in-place without making a copy of the array.

Example 1 :-

Input: nums = [0, 1, 0, 3, 12]
Output: [1, 3, 12, 0, 0]

Example 2 :-

Input: nums = [1, 0, 0, 5, 6, 9, 0]
Output: [1, 5, 6, 9, 0, 0, 0]

Solution 1

class Solution {
    
    public void moveZeroes(int[] array) {
        
        // Traverse array from left to right 
        for (int i = 0; i < array.length-1; i++) {
            
            // Check if current element is 0 or not.
            if (array[i] == 0) {
                
                // If current element is 0 then again traverse array 
                // From i+1 to last array element
                for (int j = i+1; j < array.length; j++) {

                    // If next element is non 0, 
                    // then swap j index element to i index and break inner loop.
                    if (array[j] != 0) {
                        array[i] = array[j];
                        array[j] = 0;
                        break;
                    }
                }
            }
        }
    }
}

Explanation :-

array =  [0, 1, 0, 3, 12]

• Outer for loop. i = 0, array = [0, 1, 0, 3, 12]
• array[0] == 0 becomes true.
• Inner for loop. j = 1
• array[1] != 0 becomes true.
• Swap array[0] = array[1] and assign array[1] = 0. 
• array = [1, 0, 0, 3, 12]
  
• Break inner loop.
•  i = 1, array = [1, 0, 0, 3, 12]
• array[1] == 0 becomes true.
• Inner for loop. j = 2
• array[2] != 0 becomes false.
• j = 3
  
• array[3] != 0 becomes false.
• Swap array[1] = array[3] and assign array[3] = 0. 
• array = [1, 3, 0, 0, 12]
  
• Break inner loop.
• i = 2, array = [1, 3, 0, 0, 12]
• array[2] == 0 becomes true.
• Inner for loop. j = 3
• array[3] != 0 becomes false.
• j = 4
  
• array[4] != 0 becomes false.
• Swap array[2] = array[4] and assign array[4] = 0. 
• array = [1, 3, 12, 0, 0]
  
• Break inner loop.
• i = 3, array = [1, 3, 12, 0, 0]
• array[3] == 0 becomes true.
• Inner for loop. j = 4
• array[4] != 0 becomes false.
• i = 4. condition becomes false in for loop and we got final array as below.
  

• array = [1, 3, 12, 0, 0]

Solution 2

class Solution {
    
    public void moveZeroes(int[] array) {
        
        int lastNonZeroIndex = 0;
	for (int i = 0; i < array.length; i++) {
	    if (array[i] != 0) {
	        array[lastNonZeroIndex++] = array[i];
	    }
	}

	for (int i = lastNonZeroIndex; i < array.length; i++) {
	    array[i] = 0;
	}
    }
}

Explanation :-

• Define int variable and assign value 0.
• Traverse array from left to right.
• If current element is non zero, then assign at lastNonZeroIndex variable index.
• In second for loop, put all 0 at end of array.

Solution Explanation :-

array =  [0, 1, 0, 3, 12]

• First For Loop
  
• i = 0, lastNonZeroIndex = 0
  
• array[0] != 0 becomes false.
• i = 1, lastNonZeroIndex = 0
• array[1] != 0 becomes true.
• array[0] = array[1]
• array = [1, 1 ,0, 3, 12]
  
• i = 2, lastNonZeroIndex = 1
• array[2] != 0 becomes false.
  
• i = 3, lastNonZeroIndex = 1
• array[3] != 0 becomes true.
• array[1] = array[3]
• array = [1, 3 ,0, 3, 12]
• i = 4, lastNonZeroIndex = 2
• array[4] != 0 becomes true.
• array[2] = array[4]
• array = [1, 3 ,12 , 3, 12]
• i = 5, lastNonZeroIndex = 3
  
  
• Second For Loop
  
• i = lastNonZeroIndex | i = 3
• array[3] = 0
• i = 4
• array[4] = 0
  
• array = [1, 3, 12, 0, 0]

 

Happy Coding.

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