《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：

  1 // 3.4 Implement Hanoi Tower with three stacks.

  2 #include <cstdio>

  3 #include <stack>

  4 using namespace std;

  5 

  6 class Solution {

  7 public:

  8     void initHanoiTower(int n) {

  9         int i;

 10         

 11         clearHanoiTower();

 12         

 13         for (i = n; i >= 1; --i) {

 14             s[0].push(i);

 15         }

 16     }

 17     

 18     void moveHanoiTower(int n, int from, int to) {

 19         if (from == to) {

 20             return;

 21         }

 22         

 23         if ((int)s[from].size() < n) {

 24             return;

 25         }

 26         

 27         if (n == 1) {

 28             s[to].push(s[from].top());

 29             s[from].pop();

 30             return;

 31         }

 32         

 33         int i;

 34         for (i = 0; i < 3; ++i) {

 35             b[i] = false;

 36         }

 37         b[from] = true;

 38         b[to] = true;

 39         int other;

 40         for (i = 0; i < 3; ++i) {

 41             if (!b[i]) {

 42                 other = i;

 43                 break;

 44             }

 45         }

 46 

 47         moveHanoiTower(n - 1, from, other);

 48         moveHanoiTower(1, from, to);

 49         moveHanoiTower(n - 1, other, to);

 50     }

 51     

 52     void clearHanoiTower() {

 53         int i;

 54         

 55         for (i = 0; i < 3; ++i) {

 56             while (!s[i].empty()) {

 57                 s[i].pop();

 58             }

 59         }

 60     }

 61     

 62     void printHanoiTower() {

 63         stack<int> ss[3];

 64         int i;

 65         

 66         for (i = 0; i < 3; ++i) {

 67             ss[i] = s[i];

 68             printf("Tower %d:", i + 1);

 69             while (!ss[i].empty()) {

 70                 printf(" %d", ss[i].top());

 71                 ss[i].pop();

 72             }

 73             printf("\n");

 74         }

 75     }

 76 private:

 77     stack<int> s[3];

 78     int b[3];

 79 };

 80 

 81 int main()

 82 {

 83     int n;

 84     Solution sol;

 85     

 86     while (scanf("%d", &n) == 1 && n > 0) {

 87         sol.initHanoiTower(n);

 88         

 89         printf("At the beginning:\n");

 90         sol.printHanoiTower();

 91         printf("\n");

 92 

 93         sol.moveHanoiTower(n, 0, 2);

 94         

 95         printf("At the end:\n");

 96         sol.printHanoiTower();

 97         printf("\n");

 98     }

 99     

100     return 0;

101 }