# Josephus Circle implementation using STL list

There are n people standing in a circle waiting to be executed. The counting out begins at some point in the circle and proceeds around the circle in a fixed direction. In each step, a certain number of people are skipped and the next person is executed. The elimination proceeds around the circle (which is becoming smaller and smaller as the executed people are removed), until only the last person remains, who is given freedom. Given the total number of persons n and a number k which indicates that k-1 persons are skipped and k-th person is killed in circle. The task is to choose the place in the initial circle so that you are the last one remaining and so survive. ( 0 based indexing) .**Examples :**

Input : Length of circle : n = 4 Count to choose next : k = 2 Output : 0 Input : n = 5 k = 3 Output : 3

We have already discussed different solutions of this problem (here , here and here). In this post a C++ STL based solution using list container is discussed which uses the idea of circular list.

## C++

`// CPP program to find last man standing` `#include <bits/stdc++.h>` `using` `namespace` `std;` `int` `josephusCircle(` `int` `n, ` `int` `k){` ` ` `list<` `int` `>l; ` `//creates a doubly linked list using stl container//` ` ` `for` `(` `int` `i=0;i<n;i++)` ` ` `l.push_back(i); ` `//pushes i to the end of the doubly linked list//` ` ` ` ` `auto` `it = l.begin(); ` ` ` `while` `(l.size()>1){` ` ` ` ` `for` `(` `int` `i=1;i<k;i++){` ` ` `it++;` ` ` ` ` `if` `(it==l.end()){` ` ` `//if iterator reahes the end,then we change it to begin of the list//` ` ` `it = l.begin();` ` ` `}` ` ` `}` ` ` ` ` `it = l.erase(it);` ` ` ` ` `if` `(it==l.end()){` ` ` `//if iterator reahes the end,then we change it to begin of the list//` ` ` `it = l.begin();` ` ` `}` ` ` `}` ` ` ` ` `return` `l.front(); ` `//returns front element of the list//` ` ` `}` `/* Driver program to test above functions */` `int` `main()` `{` ` ` `int` `n=14,k=2;` ` ` ` ` `cout<<josephusCircle(n,k)<<` `"\n"` `;` ` ` ` ` `return` `0;` `}` |

## Java

`// Java Code to find the last man Standing` `public` `class` `GFG {` ` ` ` ` `// Node class to store data` ` ` `static` `class` `Node` ` ` `{` ` ` `public` `int` `data ;` ` ` `public` `Node next;` ` ` `public` `Node( ` `int` `data )` ` ` `{` ` ` `this` `.data = data;` ` ` `}` ` ` `}` ` ` ` ` `/* Function to find the only person left` ` ` `after one in every m-th node is killed` ` ` `in a circle of n nodes */` ` ` `static` `void` `getJosephusPosition(` `int` `m, ` `int` `n)` ` ` `{` ` ` `// Create a circular linked list of` ` ` `// size N.` ` ` `Node head = ` `new` `Node(` `1` `);` ` ` `Node prev = head;` ` ` `for` `(` `int` `i = ` `2` `; i <= n; i++)` ` ` `{` ` ` `prev.next = ` `new` `Node(i);` ` ` `prev = prev.next;` ` ` `}` ` ` ` ` `// Connect last node to first` ` ` `prev.next = head;` ` ` ` ` `/* while only one node is left in the` ` ` `linked list*/` ` ` `Node ptr1 = head, ptr2 = head;` ` ` ` ` `while` `(ptr1.next != ptr1)` ` ` `{` ` ` ` ` `// Find m-th node` ` ` `int` `count = ` `1` `;` ` ` `while` `(count != m)` ` ` `{` ` ` `ptr2 = ptr1;` ` ` `ptr1 = ptr1.next;` ` ` `count++;` ` ` `}` ` ` ` ` `/* Remove the m-th node */` ` ` `ptr2.next = ptr1.next;` ` ` `ptr1 = ptr2.next;` ` ` `}` ` ` `System.out.println (` `"Last person left standing "` `+` ` ` `"(Josephus Position) is "` `+ ptr1.data);` ` ` `}` ` ` ` ` `/* Driver program to test above functions */` ` ` `public` `static` `void` `main(String args[])` ` ` `{` ` ` `int` `n = ` `14` `, m = ` `2` `;` ` ` `getJosephusPosition(m, n);` ` ` `}` `}` |

## Python3

`# Python3 program to find last man standing` `# /* structure for a node in circular` `# linked list */` `class` `Node:` ` ` `def` `__init__(` `self` `, x):` ` ` `self` `.data ` `=` `x` ` ` `self` `.` `next` `=` `None` `# /* Function to find the only person left` `# after one in every m-th node is killed` `# in a circle of n nodes */` `def` `getJosephusPosition(m, n):` ` ` ` ` `# Create a circular linked list of` ` ` `# size N.` ` ` `head ` `=` `Node(` `1` `)` ` ` `prev ` `=` `head` ` ` `for` `i ` `in` `range` `(` `2` `, n ` `+` `1` `):` ` ` `prev.` `next` `=` `Node(i)` ` ` `prev ` `=` `prev.` `next` ` ` `prev.` `next` `=` `head ` `# Connect last` ` ` `#node to first` ` ` `#/* while only one node is left in the` ` ` `#linked list*/` ` ` `ptr1 ` `=` `head` ` ` `ptr2 ` `=` `head` ` ` `while` `(ptr1.` `next` `!` `=` `ptr1):` ` ` `# Find m-th node` ` ` `count ` `=` `1` ` ` `while` `(count !` `=` `m):` ` ` `ptr2 ` `=` `ptr1` ` ` `ptr1 ` `=` `ptr1.` `next` ` ` `count ` `+` `=` `1` ` ` `# /* Remove the m-th node */` ` ` `ptr2.` `next` `=` `ptr1.` `next` ` ` `# free(ptr1)` ` ` `ptr1 ` `=` `ptr2.` `next` ` ` `print` `(` `"Last person left standing (Josephus Position) is "` `, ptr1.data)` `# /* Driver program to test above functions */` `if` `__name__ ` `=` `=` `'__main__'` `:` ` ` `n ` `=` `14` ` ` `m ` `=` `2` ` ` `getJosephusPosition(m, n)` `# This code is contributed by mohit kumar 29` |

## C#

`// C# Code to find the last man Standing` `using` `System;` `public` `class` `GFG {` ` ` ` ` `// Node class to store data` ` ` `class` `Node` ` ` `{` ` ` `public` `int` `data ;` ` ` `public` `Node next;` ` ` `public` `Node( ` `int` `data )` ` ` `{` ` ` `this` `.data = data;` ` ` `}` ` ` `}` ` ` ` ` `/* Function to find the only person left` ` ` `after one in every m-th node is killed` ` ` `in a circle of n nodes */` ` ` `static` `void` `getJosephusPosition(` `int` `m, ` `int` `n)` ` ` `{` ` ` `// Create a circular linked list of` ` ` `// size N.` ` ` `Node head = ` `new` `Node(1);` ` ` `Node prev = head;` ` ` `for` `(` `int` `i = 2; i <= n; i++)` ` ` `{` ` ` `prev.next = ` `new` `Node(i);` ` ` `prev = prev.next;` ` ` `}` ` ` ` ` `// Connect last node to first` ` ` `prev.next = head;` ` ` ` ` `/* while only one node is left in the` ` ` `linked list*/` ` ` `Node ptr1 = head, ptr2 = head;` ` ` ` ` `while` `(ptr1.next != ptr1)` ` ` `{` ` ` ` ` `// Find m-th node` ` ` `int` `count = 1;` ` ` `while` `(count != m)` ` ` `{` ` ` `ptr2 = ptr1;` ` ` `ptr1 = ptr1.next;` ` ` `count++;` ` ` `}` ` ` ` ` `/* Remove the m-th node */` ` ` `ptr2.next = ptr1.next;` ` ` `ptr1 = ptr2.next;` ` ` `}` ` ` `Console.WriteLine (` `"Last person left standing "` `+` ` ` `"(Josephus Position) is "` `+ ptr1.data);` ` ` `}` ` ` ` ` `/* Driver program to test above functions */` ` ` `static` `public` `void` `Main(String []args)` ` ` `{` ` ` `int` `n = 14, m = 2;` ` ` `getJosephusPosition(m, n);` ` ` `}` `}` `//contributed by Arnab Kundu` |

## Javascript

`<script>` `// javascript Code to find the last man Standing` ` ` ` ` `// Node class to store data` `class Node {` ` ` `constructor(val) {` ` ` `this` `.data = val;` ` ` `this` `.next = ` `null` `;` ` ` `}` `}` ` ` `/*` ` ` `* Function to find the only person left after one in every m-th node is killed` ` ` `* in a circle of n nodes` ` ` `*/` ` ` `function` `getJosephusPosition(m , n) {` ` ` `// Create a circular linked list of` ` ` `// size N.` `var` `head = ` `new` `Node(1);` `var` `prev = head;` ` ` `for` `(i = 2; i <= n; i++) {` ` ` `prev.next = ` `new` `Node(i);` ` ` `prev = prev.next;` ` ` `}` ` ` `// Connect last node to first` ` ` `prev.next = head;` ` ` `/*` ` ` `* while only one node is left in the linked list` ` ` `*/` `var` `ptr1 = head, ptr2 = head;` ` ` `while` `(ptr1.next != ptr1) {` ` ` `// Find m-th node` ` ` `var` `count = 1;` ` ` `while` `(count != m) {` ` ` `ptr2 = ptr1;` ` ` `ptr1 = ptr1.next;` ` ` `count++;` ` ` `}` ` ` `/* Remove the m-th node */` ` ` `ptr2.next = ptr1.next;` ` ` `ptr1 = ptr2.next;` ` ` `}` ` ` `document.write(` `"Last person left standing "` `+ ` `"(Josephus Position) is "` `+ ptr1.data);` ` ` `}` ` ` `/* Driver program to test above functions */` ` ` ` ` `var` `n = 14, m = 2;` ` ` `getJosephusPosition(m, n);` `// This code is contributed by umadevi9616` `</script>` |

**Output**

12

**Output : **

Last person left standing (Josephus Position) is 12 ( 0 based indexing )

**Time complexity:** O(k * n)

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