130.cpp

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// 130.cpp http://acm.uva.es/p/v1/130.html
//
// Solution to ACM problem #130 - "Roman Roulette"
//
// Matthew Eagar - meagar@gmail.com
// Verified to work as of Feb 19 / 2005
#include <iostream>
struct Person {
int id;
Person* next;
Person* prev;
};
Person * makeRing(int n) {
Person* base = new Person;
Person* current = base;
for (int i = 1; i <= n; ++i) {
current->id = i;
if (i != n) {
current->next = new Person;
current->next->prev = current;
current = current->next;
}
}
// link the last guy back to the first
current->next = base;
base->prev = current;
return base;
}
int main() {
int n = 0;
int k = 0;
while (std::cin >> n >> k) {
if (n == 0 && k == 0) return 0;
if (n == 0) {
std::cout << n << std::endl;
continue;
}
// setup our people
Person* basePerson = makeRing(n);
Person* dead = basePerson;
Person* digger = 0;
// find the dead person
for (int i = 0; i < k - 1; ++i) {
dead = dead->next;
}
for (int numLeft = n; numLeft > 1; --numLeft) {
// remove the dead person
dead->prev->next = dead->next;
dead->next->prev = dead->prev;
// find the digger
digger = dead;
for (int i = 0; i < k; ++i)
digger = digger->next;
//swap the digger for the dead guy;
dead->id = digger->id;
// restore the links
dead->prev->next = dead;
dead->next->prev = dead;
digger->prev->next = digger->next;
digger->next->prev = digger->prev;
delete digger;
for (int i = 0; i < k; ++i)
dead = dead->next;
}
// 'dead' now points to the only living guy :/
int startPos = 1;
int winner = dead->id;
while (winner != 1) {
--startPos;
if (startPos < 1) startPos = n;
--winner;
}
std::cout << startPos << std::endl;
}
}