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Minimize a binary string by repeatedly removing even length substrings of same characters
  • Difficulty Level : Hard
  • Last Updated : 18 Dec, 2020

Given a binary string str of size N, the task is to minimize the length of given binary string by removing even length substrings consisting of sam characters, i.e. either 0s or 1s only, from the string any number of times. Finally, print the modified string.

Examples:

Input: str =”101001″
Output: “10”
Explanation: The string can be minimized in the following manner: “101001″ -> “1011” -> “10”.

Input: str = “00110”
Output: “0”
Explanation: The string can be minimized in the following manner: “00110″ -> “110″ -> “0”.

Approach: The idea is to use a stack to solve the problem. While traversing the string, if the current character is found to be same as the top element of the stack, pop the element from the stack. After traversal, print the stack from bottom to top. Follow the steps below to solve the problem:



Below is the implementation of the above approach.

C++

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// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Recursive function to print stack
// elements from bottom to top without
// changing their order
void PrintStack(stack<char> s)
{
    // If stack is empty
    if (s.empty())
        return;
 
    char x = s.top();
 
    // Pop top element of the stack
    s.pop();
 
    // Recursively call the
    // function PrintStack
    PrintStack(s);
 
    // Print the stack element
    // from the bottom
    cout << x;
 
    // Push the same element onto the
    // stack to preserve the order
    s.push(x);
}
 
// Function to minimize binary string
// by removing substrings consisting
// of same character
void minString(string s)
{
    // Declare a stack of characters
    stack<char> Stack;
 
    // Push the first character of
    // the string into the stack
    Stack.push(s[0]);
 
    // Traverse the string s
    for (int i = 1; i < s.size(); i++) {
 
        // If Stack is empty
        if (Stack.empty()) {
 
            // Push current character
            // into the stack
            Stack.push(s[i]);
        }
 
        else {
 
            // Check if the current
            // character is same as
            // the top of the stack
            if (Stack.top() == s[i]) {
 
                // If true, pop the
                // top of the stack
                Stack.pop();
            }
 
            // Otherwise, push the
            // current element
            else {
                Stack.push(s[i]);
            }
        }
    }
 
    // Print stack from bottom to top
    PrintStack(Stack);
}
 
// Driver Code
int main()
{
    string str = "101001";
    minString(str);
 
    return 0;
}

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Java

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// Java program for the above approach
import java.util.*;
 
class GFG{
 
// Recursive function to print stack
// elements from bottom to top without
// changing their order
static void PrintStack(Stack<Character> s)
{
    // If stack is empty
    if (s.isEmpty())
        return;
 
    char x = s.peek();
 
    // Pop top element of the stack
    s.pop();
 
    // Recursively call the
    // function PrintStack
    PrintStack(s);
 
    // Print the stack element
    // from the bottom
    System.out.print(x);
 
    // Push the same element onto the
    // stack to preserve the order
    s.add(x);
}
 
// Function to minimize binary String
// by removing subStrings consisting
// of same character
static void minString(String s)
{
    // Declare a stack of characters
    Stack<Character> Stack = new Stack<Character>();
 
    // Push the first character of
    // the String into the stack
    Stack.add(s.charAt(0));
 
    // Traverse the String s
    for (int i = 1; i < s.length(); i++) {
 
        // If Stack is empty
        if (Stack.isEmpty()) {
 
            // Push current character
            // into the stack
            Stack.add(s.charAt(i));
        }
 
        else {
 
            // Check if the current
            // character is same as
            // the top of the stack
            if (Stack.peek() == s.charAt(i)) {
 
                // If true, pop the
                // top of the stack
                Stack.pop();
            }
 
            // Otherwise, push the
            // current element
            else {
                Stack.push(s.charAt(i));
            }
        }
    }
 
    // Print stack from bottom to top
    PrintStack(Stack);
}
 
// Driver Code
public static void main(String[] args)
{
    String str = "101001";
    minString(str);
 
}
}
 
// This code is contributed by Amit Katiyar

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Python3

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# Python3 program for the above approach
 
# Recursive function to print stack
# elements from bottom to top without
# changing their order
def PrintStack(s) :
 
    # If stack is empty
    if (len(s) == 0) :
        return;
 
    x = s[-1];
 
    # Pop top element of the stack
    s.pop();
 
    # Recursively call the
    # function PrintStack
    PrintStack(s);
 
    # Print the stack element
    # from the bottom
    print(x, end="");
 
    # Push the same element onto the
    # stack to preserve the order
    s.append(x);
 
# Function to minimize binary string
# by removing substrings consisting
# of same character
def minString(s) :
 
    # Declare a stack of characters
    Stack = [];
 
    # Push the first character of
    # the string into the stack
    Stack.append(s[0]);
 
    # Traverse the string s
    for i in range(1, len(s)) :
 
        # If Stack is empty
        if (len(Stack) == 0) :
 
            # Push current character
            # into the stack
            Stack.append(s[i]);
 
        else:
 
            # Check if the current
            # character is same as
            # the top of the stack
            if (Stack[-1] == s[i]) :
 
                # If true, pop the
                # top of the stack
                Stack.pop();
 
            # Otherwise, push the
            # current element
            else :
                Stack.append(s[i]);
 
    # Print stack from bottom to top
    PrintStack(Stack);
 
# Driver Code
if __name__ == "__main__" :
 
    string = "101001";
    minString(string);
 
    # This code is contributed by AnkThon

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C#

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// C# program for the above approach
using System;
using System.Collections.Generic;
class GFG
{
 
// Recursive function to print stack
// elements from bottom to top without
// changing their order
static void PrintStack(Stack<char> s)
{
    // If stack is empty
    if (s.Count == 0)
        return;
    char x = s.Peek();
 
    // Pop top element of the stack
    s.Pop();
 
    // Recursively call the
    // function PrintStack
    PrintStack(s);
 
    // Print the stack element
    // from the bottom
    Console.Write((char)x);
 
    // Push the same element onto the
    // stack to preserve the order
    s.Push(x);
}
 
// Function to minimize binary String
// by removing subStrings consisting
// of same character
static void minString(String s)
{
    // Declare a stack of characters
    Stack<char> Stack = new Stack<char>();
 
    // Push the first character of
    // the String into the stack
    Stack.Push(s[0]);
 
    // Traverse the String s
    for (int i = 1; i < s.Length; i++)
    {
 
        // If Stack is empty
        if (Stack.Count == 0)
        {
 
            // Push current character
            // into the stack
            Stack.Push(s[i]);
        }
 
        else
        {
 
            // Check if the current
            // character is same as
            // the top of the stack
            if (Stack.Peek() == s[i])
            {
 
                // If true, pop the
                // top of the stack
                Stack.Pop();
            }
 
            // Otherwise, push the
            // current element
            else
            {
                Stack.Push(s[i]);
            }
        }
    }
 
    // Print stack from bottom to top
    PrintStack(Stack);
}
 
// Driver Code
public static void Main(String[] args)
{
    String str = "101001";
    minString(str);
}
}
 
// This code is contributed by 29AjayKumar

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Output: 

10

 

Time Complexity: O(N)
Auxiliary Space: O(N)

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