Delete middle element of a stack
Given a stack with push(), pop(), empty() operations, delete middle of it without using any additional data structure.
Input : Stack[] = [1, 2, 3, 4, 5] Output : Stack[] = [1, 2, 4, 5] Input : Stack[] = [1, 2, 3, 4, 5, 6] Output : Stack[] = [1, 2, 4, 5, 6]
The idea is to use recursive calls. We first remove all items one by one, then we recur. After recursive calls, we push all items back except the middle item.
C++
// C++ code to delete middle of a stack // without using additional data structure. #include<bits/stdc++.h> using namespace std; // Deletes middle of stack of size // n. Curr is current item number void deleteMid(stack<char> &st;, int n, int curr=0) { // If stack is empty or all items // are traversed if (st.empty() || curr == n) return; // Remove current item int x = st.top(); st.pop(); // Remove other items deleteMid(st, n, curr+1); // Put all items back except middle if (curr != n/2) st.push(x); } //Driver function to test above functions int main() { stack<char> st; //push elements into the stack st.push('1'); st.push('2'); st.push('3'); st.push('4'); st.push('5'); st.push('6'); st.push('7'); deleteMid(st, st.size()); // Printing stack after deletion // of middle. while (!st.empty()) { char p=st.top(); st.pop(); cout << p << " "; } return 0; } |
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Java
// Java code to delete middle of a stack // without using additional data structure. import java.io.*; import java.util.*; public class GFG { // Deletes middle of stack of size // n. Curr is current item number static void deleteMid(Stack<Character> st, int n, int curr) { // If stack is empty or all items // are traversed if (st.empty() || curr == n) return; // Remove current item char x = st.pop(); // Remove other items deleteMid(st, n, curr+1); // Put all items back except middle if (curr != n/2) st.push(x); } // Driver function to test above functions public static void main(String args[]) { Stack<Character> st = new Stack<Character>(); // push elements into the stack st.push('1'); st.push('2'); st.push('3'); st.push('4'); st.push('5'); st.push('6'); st.push('7'); deleteMid(st, st.size(), 0); // Printing stack after deletion // of middle. while (!st.empty()) { char p=st.pop(); System.out.print(p + " "); } } } // This code is contributed by // Manish Shaw (manishshaw1) |
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Python3
# Python3 code to delete middle of a stack # without using additional data structure. # Deletes middle of stack of size # n. Curr is current item number class Stack: def __init__(self): self.items = [] def isEmpty(self): return self.items == [] def push(self, item): self.items.append(item) def pop(self): return self.items.pop() def peek(self): return self.items[len(self.items)-1] def size(self): return len(self.items) def deleteMid(st, n, curr) : # If stack is empty or all items # are traversed if (st.isEmpty() or curr == n) : return # Remove current item x = st.peek() st.pop() # Remove other items deleteMid(st, n, curr+1) # Put all items back except middle if (curr != int(n/2)) : st.push(x) # Driver function to test above functions st = Stack() # push elements into the stack st.push('1') st.push('2') st.push('3') st.push('4') st.push('5') st.push('6') st.push('7') deleteMid(st, st.size(), 0) # Printing stack after deletion # of middle. while (st.isEmpty() == False) : p = st.peek() st.pop() print (str(p) + " ", end="") # This code is contributed by # Manish Shaw (manishshaw1) |
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C#
// C# code to delete middle of a stack // without using additional data structure. using System; using System.Collections.Generic; class GFG { // Deletes middle of stack of size // n. Curr is current item number static void deleteMid(Stack<char> st, int n, int curr = 0) { // If stack is empty or all // items are traversed if (st.Count == 0 || curr == n) return; // Remove current item char x = st.Peek(); st.Pop(); // Remove other items deleteMid(st, n, curr+1); // Put all items // back except middle if (curr != n / 2) st.Push(x); } // Driver Code public static void Main() { Stack<char> st = new Stack<char>(); // push elements into the stack st.Push('1'); st.Push('2'); st.Push('3'); st.Push('4'); st.Push('5'); st.Push('6'); st.Push('7'); deleteMid(st, st.Count); // Printing stack after // deletion of middle. while (st.Count != 0) { char p=st.Peek(); st.Pop(); Console.Write(p + " "); } } } // This code is contributed by // Manish Shaw (manishshaw1) |
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Output:
7 6 5 3 2 1
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