Largest Rectangle In Histogram InterviewBit/ LeetCode

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 class StoreStack{

    int data;
    int val;
}


public class Solution {
    public int largestRectangleArea(int[] arr) {

        int n=arr.length;
        Stack<StoreStack> stack1=new Stack<StoreStack>(); 
        Stack<StoreStack> stack2=new Stack<StoreStack>(); 
        
        ArrayList<Integer>aa=new ArrayList<Integer>();
        ArrayList<Integer>ab=new ArrayList<Integer>();
        ArrayList<Integer>ac=new ArrayList<Integer>();
        
        StoreStack obj[]=new StoreStack[n];
        
        for(int i=0;i<n;i++){
            obj[i]=new StoreStack();
            obj[i].data=arr[i];
            obj[i].val=i;
            
        }
        
        for(int i=0;i<n;i++){
            if(stack1.isEmpty()){
                aa.add(-1);
            }
            else{
                if(stack1.peek().data<arr[i]){
                    aa.add(stack1.peek().val);
                }
                else{
                    while(!stack1.isEmpty() && stack1.peek().data>=arr[i]){
                        stack1.pop();
                    }
                    if(stack1.isEmpty()){
                        aa.add(-1);
                    }
                    else{
                        aa.add(stack1.peek().val);
                    }
                }
            }
            stack1.push(obj[i]);
        }
        
        //System.out.println("Left: "+aa+" ");
        
        
        
        for(int i=n-1;i>-1;i--){
            if(stack2.isEmpty()){
                ab.add(n);
            }
            else{
                if(stack2.peek().data<arr[i]){
                    ab.add(stack2.peek().val);
                }
                else{
                    while(!stack2.isEmpty() && stack2.peek().data>=arr[i]){
                        stack2.pop();
                    }
                    if(stack2.isEmpty()){
                        ab.add(n);
                    }
                    else{
                        ab.add(stack2.peek().val);
                    }
                }
            }
            stack2.push(obj[i]);
        }
        Collections.reverse(ab);
        //System.out.println("Right: "+ab+" ");
        
        //System.out.println("New ArrayList will be ac: ");
        
        for(int i=0;i<n;i++){
            ac.add(ab.get(i)-aa.get(i)-1);
        }
        
        for(int i=0;i<n;i++){
            ac.set(i,ac.get(i)*arr[i]);
        }
        //System.out.println("Final: "+ac+" ");
        
        //System.out.println("Max Area: "+Collections.max(ac));
        
        return   Collections.max(ac);

    }
}


TIME:O(N) [Using Single Loop][LeetCode Time:76ms faster than 17.43%]

SPACE:O(N) [Using ArrayList][LeetCode Space: 53.7MB less than 47.64%]

/*Memory can further be enhanced using the same stack ie stack1 and
using ArrayList ab instead of ArrayList ac.*/


Thanks For Reading.😇

"Share Further To Increase Knowledge Treasure."😊

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