每天一个小算法（6）---- 通过两个栈实现一个队列

这个算法也很简单，定义两个栈m_aStack、m_bStack，m_aStack负责push()数据，m_bStack负责front()数据。

思路：每一次front()取数据都会检查一下m_bStack是否为空，为空则把m_aStack的所有数据pop()出来push()到m_bStack中。

因为STL里有stack，直接拿来用了，代码使用C++，在linux/g++下编译运行成功：

  1 #include <stack>
  2 #include <stdio.h>
  3 #include <stdlib.h>
  4 #include <time.h>
  5
  6 class Fifo
  7 {
  8 public:
  9     const int size() const;
 10     const bool empty() const;
 11     const int front();
 12     void push(int element);
 13     void print() const;
 14 private:
 15     std::stack<int> m_aStack;
 16     std::stack<int> m_bStack;
 17 };
 18
 19 const int Fifo::size() const
 20 {
 21     return m_aStack.size() + m_bStack.size();
 22 }
 23
 24 const bool Fifo::empty() const
 25 {
 26     return m_aStack.empty() & m_bStack.empty();
 27 }
 28
 29 const int Fifo::front()
 30 {
 31     if( empty() )
 32         return 0;
 33
 34     if ( m_bStack.empty() )
 35     {
 36         while ( !m_aStack.empty() )
 37         {
 38             m_bStack.push(m_aStack.top());
 39             m_aStack.pop();
 40         }
 41     }
 42
 43     int tmp = m_bStack.top();
 44     m_bStack.pop();
 45     return tmp;
 46 }
 47
 48 void Fifo::push(int element)
 49 {
 50     m_aStack.push(element);
 51 }
 52
 53 void Fifo::print() const
 54 {
 55     if ( empty() )
 56         return;
 57
 58     std::stack<int> tAStack = m_aStack;
 59     std::stack<int> tBStack = m_bStack;
 60
 61     printf("the elements of the m_aStack:\t");
 62     while ( !tAStack.empty() )
 63     {
 64         printf("%d ", tAStack.top());
 65         tAStack.pop();
 66     }
 67     printf("\n");
 68
 69     printf("the elements of the m_bStack:\t");
 70     while ( !tBStack.empty() )
 71     {
 72         printf("%d ", tBStack.top());
 73         tBStack.pop();
 74     }
 75     printf("\n");
 76
 77 }
 78
 79 int main(int argc, char const *argv[])
 80 {
 81     Fifo fifo;
 82     srand((int)time(0));
 83     for ( int i=0; i< 100; ++i )
 84     {
 85         if ( (rand() & 1) == 0 )
 86         {
 87             int tmp = rand()%100;
 88             printf("\npush %d to fifo\n", tmp);
 89             fifo.push(tmp);
 90             fifo.print();
 91         }
 92         else
 93         {
 94             printf("\nthe front of the fifo: %d\n", fifo.front());
 95             fifo.print();
 96         }
 97     }
 98
 99     return 0;
100 }

每天一个小算法（6）---- 通过两个栈实现一个队列