《Cracking the Coding Interview》——第3章：栈和队列——题目4

2014-03-18 05:28

题目：你肯定听过汉诺威塔的故事：三个柱子和N个从小到大的盘子。既然每次你只能移动放在顶上的盘子，这不就是栈操作吗？所以，请用三个栈来模拟N级汉诺威塔的玩法。放心，N不会很大的。

解法：递归着玩儿吧，还挺容易写的。要是迭代，我估计够呛。

代码：

 // 3.4 Implement Hanoi Tower with three stacks.
 #include <cstdio>
 #include <stack>
 using namespace std;

 class Solution {
 public:
     void initHanoiTower(int n) {
         int i;

         clearHanoiTower();

         for (i = n; i >= ; --i) {
             s[].push(i);
         }
     }

     void moveHanoiTower(int n, int from, int to) {
         if (from == to) {
             return;
         }

         if ((int)s[from].size() < n) {
             return;
         }

         if (n == ) {
             s[to].push(s[from].top());
             s[from].pop();
             return;
         }

         int i;
         for (i = ; i < ; ++i) {
             b[i] = false;
         }
         b[from] = true;
         b[to] = true;
         int other;
         for (i = ; i < ; ++i) {
             if (!b[i]) {
                 other = i;
                 break;
             }
         }

         moveHanoiTower(n - , from, other);
         moveHanoiTower(, from, to);
         moveHanoiTower(n - , other, to);
     }

     void clearHanoiTower() {
         int i;

         for (i = ; i < ; ++i) {
             while (!s[i].empty()) {
                 s[i].pop();
             }
         }
     }

     void printHanoiTower() {
         stack<int> ss[];
         int i;

         for (i = ; i < ; ++i) {
             ss[i] = s[i];
             printf("Tower %d:", i + );
             while (!ss[i].empty()) {
                 printf(" %d", ss[i].top());
                 ss[i].pop();
             }
             printf("\n");
         }
     }
 private:
     stack<int> s[];
     int b[];
 };

 int main()
 {
     int n;
     Solution sol;

     while (scanf("%d", &n) ==  && n > ) {
         sol.initHanoiTower(n);

         printf("At the beginning:\n");
         sol.printHanoiTower();
         printf("\n");

         sol.moveHanoiTower(n, , );

         printf("At the end:\n");
         sol.printHanoiTower();
         printf("\n");
     }

     return ;
 }