Next Greater Element Geeks For Geeks And InterviewBit

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 Approach 1: Using ArrayList

        

        ArrayList<Long> aa=new ArrayList<Long>();

        Stack<Long>stack=new Stack<Long>();

        for(int i=n-1;i>-1;i--){

            if(stack.isEmpty()==true){

                aa.add(Long.valueOf(-1));

            }

            else{

                if(stack.peek()>arr[i]){

                    aa.add(stack.peek());

                }

                else{

                    while(!stack.isEmpty() && stack.peek()<=arr[i]){

                        stack.pop();

                    }

                    if(stack.isEmpty()==true){

                        aa.add(Long.valueOf(-1));

                    }

                    else{

                        aa.add(stack.peek());

                    }

                }

                

            }

            stack.push(arr[i]);

        }

        Collections.reverse(aa);

        long arr1[]=new long[aa.size()];

        for(int i=0;i<aa.size();i++){

            arr1[i]=aa.get(i);

        }

        return arr1;


TIME:O(N)[GFG Time:2.9/4.6][Not Exactly Sure, Near About This Range]

SPACE:O(N)[Array And ArrayList Both Are Used]




*********************************************************************************


Approach 2: Using Array Directly

        

        ArrayList<Long> aa=new ArrayList<Long>();

        Stack<Long>stack=new Stack<Long>();

         long arr1[]=new long[arr.length];

         

        for(int i=n-1;i>-1;i--){

            if(stack.isEmpty()==true){

                arr1[i]=(Long.valueOf(-1));

            }

            else{

                if(stack.peek()>arr[i]){

                    arr1[i]=(stack.peek());

                }

                else{

                    while(!stack.isEmpty() && stack.peek()<=arr[i]){

                        stack.pop();

                    }

                    if(stack.isEmpty()==true){

                        arr1[i]=(Long.valueOf(-1));

                    }

                    else{

                        arr1[i]=(stack.peek());

                    }

                }

                

            }

            stack.push(arr[i]);

        }

      

        for(int i=0;i<n/2;i++){

            long temp=arr[i];

            arr[i]=arr[n-i-1];

            arr[n-i-1]=temp;

        }

        

        return arr1;

        

TIME:O(N)[GFG Time:2.9/4.6][Sure]

SPACE:O(N)[Array Is Used Only]


***********************************************************************************

InterviewBit:


public class Solution {
    public int[] nextGreater(int[] arr) {
         ArrayList<Integer> aa=new ArrayList<Integer>();

        Stack<Integer>stack=new Stack<Integer>();

         int arr1[]=new int[arr.length];

        int n=arr.length;
         

        for(int i=n-1;i>-1;i--){

            if(stack.isEmpty()==true){

                arr1[i]=(-1);

            }

            else{

                if(stack.peek()>arr[i]){

                    arr1[i]=(stack.peek());

                }

                else{

                    while(!stack.isEmpty() && stack.peek()<=arr[i]){

                        stack.pop();

                    }

                    if(stack.isEmpty()==true){

                        arr1[i]=-1;

                    }

                    else{

                        arr1[i]=(stack.peek());

                    }

                }

                

            }

            stack.push(arr[i]);

        }

      

        for(int i=0;i<n/2;i++){

            int temp=arr[i];

            arr[i]=arr[n-i-1];

            arr[n-i-1]=temp;

        }

        

        return arr1;

        


    }
}





Thanks For Reading.😇

"Share Further To Increase Knowledge Treasure.😊"


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