096_LastNumberInCircle.cpp

// Coding Interviews: Questions, Analysis & Solutions
// Harry He

#include <stdio.h>
#include <list>

using namespace std;

// ==================== Solution 1====================
int LastRemaining_Solution1(unsigned int n, unsigned int m)
{
    if(n < 1 || m < 1)
        return -1;

    list<int> numbers;
    for(unsigned int i = 0; i < n; ++ i)
        numbers.push_back(i);

    list<int>::iterator current = numbers.begin();
    while(numbers.size() > 1)
    {
        for(int i = 1; i < m; ++ i)
        {
            current ++;
            if(current == numbers.end())
                current = numbers.begin();
        }

        list<int>::iterator next = ++ current;
        if(next == numbers.end())
            next = numbers.begin();

        -- current;
        numbers.erase(current);
        current = next;
    }

    return *(current);
}

// ==================== Solution 2 ====================
int LastRemaining_Solution2(unsigned int n, unsigned int m)
{
    if(n < 1 || m < 1)
        return -1;

    int last = 0;
    for (int i = 2; i <= n; i ++) 
        last = (last + m) % i;

    return last;
}

// ==================== Test Code ====================
void Test(char* testName, unsigned int n, unsigned int m, int expected)
{
    if(testName != NULL)
        printf("%s begins: \n", testName);

    if(LastRemaining_Solution1(n, m) == expected)
        printf("Solution1 passed.\n");
    else
        printf("Solution1 failed.\n");

    if(LastRemaining_Solution2(n, m) == expected)
        printf("Solution2 passed.\n");
    else
        printf("Solution2 failed.\n");

    printf("\n");
}

void Test1()
{
    Test("Test1", 5, 3, 3);
}

void Test2()
{
    Test("Test2", 5, 2, 2);
}

void Test3()
{
    Test("Test3", 6, 7, 4);
}

void Test4()
{
    Test("Test4", 6, 6, 3);
}

void Test5()
{
    Test("Test5", 0, 0, -1);
}

void Test6()
{
    Test("Test6", 4000, 997, 1027);
}

int main(int argc, char* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();

    return 0;
}