Solving codingBat Post4 with one loop in Java

Question

The question is about Solving this problem from codingBat in Java.

Problem Statement:

Given a non-empty array of ints, return a new array containing the elements from the original array that come after the last 4 in the original array. The original array will contain at least one 4. Note that it is valid in Java to create an array of length 0.

post4({2, 4, 1, 2}) → {1, 2}

post4({4, 1, 4, 2}) → {2}

post4({4, 4, 1, 2, 3}) → {1, 2, 3}

Here is my solution:

public int[] post4(int[] nums) {

int lastFour=-1;
int[] post4={};

  for(int i=nums.length-1;i>=0;i--)
  {
     if((nums[i]==4))
     {
       lastFour=i;    //find the index of the last 4 in the array
       break;
     }  
   } 
   int newLen=(nums.length-lastFour)-1;
   post4=new int[newLen];   //reassign the post4 array with required length

  for(int j=0;j<newLen;j++)
  {
     post4[j]=nums[lastFour+1];   //assign values from orig. array after last 4
     lastFour++;
  }

  return post4;   
}

But I have used 2 loops. It should be solved using at max one loop. Do not use collections or any wrappers classes.

Answer 1

• Before iteration create result array, lets say with length 0.
• Each time you find 4 create new result array with size based on index of that 4 and length of nums to store rest of elements.
• If number is not 4 place it in result array (don't place if result arrays length is 0 because it means we didn't find any 4 yet, or it was last element of nums array).

Here is example solution

public int[] post4(int[] nums) {

    int[] result = new int[0];

    int j = 0;
    for (int i = 0; i<nums.length; i++){
       if (nums[i] == 4) {
           result = new int[nums.length - i-1];
           j=0;
       }
       else 
           if (result.length>0) result[j++] = nums[i]; 
    }

    return result;
}

Answer 2

You may use the class Arrays...that is:

public int[] post4(int[] nums) {
    int lastFourIndex = 0;
      for (int i = 0; i < nums.length; i++) {

          if(nums[i] == 4)
          {
              lastFourIndex = i;
          }
    }
      return Arrays.copyOfRange(nums, lastFourIndex+1, nums.length);
}

Angelo