Array Division to Three Stacks LeetCode (Creating 3 Stacks with 1 Array)

Given an array, divide it into 3 stacks. You need to implement the push, peek, and pop methods similar to basic Stack.

1. push(Stack st, int a): The push operation will be given the stack to push and the value to push.
2. pop(Stack st): The pop operation will be given the stack to pop from.
3. peek(Stack st): The peek operation will be given the stack to pop from.

The underlying array should be used to act as Stack and operate the push, pop, and peek methods as defined above.

This problem is simple array manipulation problem and is well discussed in several forums, such as StackOverFlow and GeeksForGeeks A collection of hundreds of interview questions and solutions are available in our blog at Interview Question

Solution

	/**
	Array division into three stacks:
	Method1:
	- we use fixed size of an array and allow size/3 lenght of an arry to each stack, so the first stack
	will be using the space 0-size/3, second stack size/3-2*size/3, and third stack 2*size/3-size.
	-the main problem with this approach is that some stack will be exhausted and some can have empty spaces
	*/
	import java.util.Arrays;
	import java.lang.Exception;
	public class ArrayDivisionToStack{
	//lets create an array assuming each stack will have 10 elements
	static int stackSize = 10;
	static int[] arr = new int[stackSize*3];
	static int[] stackIndices = {-1, -1, -1}; //these are the indices that point to the top element of each stack
	//method to push element into stack
	public static void push(int stack, int val) throws Exception{
	System.out.println("pushing item :"+val+" to stack:"+stack);
	if(stackIndices[stack]<stackSize-1){
	arr[++stackIndices[stack]+stack*stackSize] = val;
	}else{
	throw new Exception("Stack "+stack+" is full:");
	}
	}
	//pop value from the top of the given stack
	public static int pop(int stack) throws Exception{
	System.out.println("popping element from stack:"+stack);
	if(stackIndices[stack]>=0){
	int item = arr[stackIndices[stack] + stack*stackSize];
	//clear the position
	arr[stackIndices[stack] + stack*stackSize] = 0;
	stackIndices[stack]--;
	return item;
	}
	else{
	throw new Exception("Stack "+stack+" is empty");
	}
	}
	//peek value from the top of the given stack
	public static int peek(int stack) throws Exception{
	System.out.println("peeking element from stack:"+stack);
	if(stackIndices[stack]>=0){
	int item = arr[stackIndices[stack] + stack*stackSize];
	return item;
	}
	else{
	throw new Exception("Stack "+stack+" is empty");
	}
	}
	public static void main(String args[]) throws Exception{
	System.out.println(Arrays.toString(arr));
	//push item to some stacks
	for(int i=0;i<11;i++)
	push(0,i);
	System.out.println(Arrays.toString(stackIndices));
	System.out.println(Arrays.toString(arr));
	pop(2);
	System.out.println(Arrays.toString(arr));
	}
	}

view raw ArrayDivisionToThreeStacks.java hosted with ❤ by GitHub