Stack – Reverse a String using Stack

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Introduction

Learn how to reverse a String using Stack. In this example takes in an array based Stack.

Stack – Data Structure – Array-based and Linked list based implementation.

The followings are the steps to reversing a String using Stack.

String to Char[].
Create a Stack.
Push all characters, one by one.
Then Pop all characters, one by one and put into the char[].
Finally, convert to the String.

public static String reverse(String str) {
        char[] charArr = str.toCharArray();
        int size = charArr.length;
        Stack stack = new Stack(size);

        int i;
        for(i = 0; i < size; ++i) {
            stack.push(charArr[i]);
        }

        for(i = 0; i < size; ++i) {
            charArr[i] = stack.pop();
        }

        return String.valueOf(charArr);
}

Time complexity – O(n)

Space complexity – O(n)

Complete Example

class Stack {
    private int top;
    private int capacity;
    private char[] array;
    public Stack(int capacity) {
        this.capacity = capacity;
        this.array = new char[capacity];
        this.top = -1;
    }
    public boolean isFull() {
        return this.top == this.capacity - 1;
    }
    public boolean isEmpty() {
        return this.top == -1;
    }
    public void push(char value) {
        if(!this.isFull()) {
            this.array[++this.top] = value;
        }
    }
    public char pop() {
        return this.isEmpty()?'\u0000':this.array[this.top--];
    }
    public static String reverse(String str) {
        char[] charArr = str.toCharArray();
        int size = charArr.length;
        Stack stack = new Stack(size);
        int i;
        for(i = 0; i < size; ++i) {
            stack.push(charArr[i]);
        }
        for(i = 0; i < size; ++i) {
            charArr[i] = stack.pop();
        }
        return String.valueOf(charArr);
    }
}
public class Main {
  public static void main(String[] args) {
      String str = "MYDEVGEEK";