栈改递归

 

递归旧问题

       这个问题，距今有3年多了。不过我自己早就忘了，以前的工程也找不到了。只好自己重新新写。本以为是个很容易的问题。实际上却花了3个多小时。

先把代码贴出来，以后腾出时间再写总结。

/*-------------------------------------------------------------------

       http://topic.youkuaiyun.com/t/20030118/19/1372004.html

       算法问题（栈改递归其它非递归方法也可！！）

       liuxk99 (极地狐)      2003-01-18 19:32:13 在 C/C++ / C语言 提问

       非递归算法实现一个函数.

              f = n; (m <= 1)

              f = m; (n <= 1)  

              f = f(m - 1, n) + f(m, n - 1); (m > 1, n > 1)

-------------------------------------------------------------------*/

#include "stdio.h"

#include "string.h"

 

#include "windows.h"

 

#define TRUE       1

#define FALSE     0

#define STACK_SIZE 1000

 

typedef struct _st{

       int m;

       int n;

       int bLeft;

       int bRight;

       int fpos; // 父节点

}st;

 

int f(int m, int n)

{

       if (m <= 1)

              return n;

       else if (n <= 1)

              return m;

       else

              return f(m - 1, n) + f(m, n - 1);

}

 

int fs(int m, int n)

{

       int res = 0;

       st stk[STACK_SIZE];

       int pos = 0, x, y, lspos;

       memset (&stk, 0, sizeof(stk));

       stk[pos].m = m;

       stk[pos].n = n;

       stk[pos].bLeft = FALSE;

       stk[pos].bRight = FALSE;

       lspos = pos;

 

       while (1)

       {

              if (stk[0].bLeft && stk[0].bRight)

                     break;

 

              printf(("/r/nstack :"));

              for (int i = 0; i <= pos; i++)

              {

                     printf (" (%d, %d)", stk[i].m, stk[i].n);

              }

              // get stack top

              x = stk[pos].m;

              y = stk[pos].n;

 

              if (x <= 1)

              {

                     lspos = stk[pos].fpos;

                     res += y;

                     stk[lspos].bLeft = TRUE;

                     printf ("/r/n%02d.Pop(%d, %d)", pos, stk[pos].m, stk[pos].n);

                     --pos; // pop stack

                     //printf(("/r/nfs(%d, %d) = %d", x, y, res);

              }

              else if (y <= 1)

              {

                     lspos = stk[pos].fpos;

                     res += x;

                     stk[lspos].bRight = TRUE;

                     printf ("/r/n%02d.Pop(%d, %d)", pos, stk[pos].m, stk[pos].n);

                     --pos; // pop stack

              }

              else

              {

                     // pop stack

                     if (stk[pos].bLeft && stk[pos].bRight)

                     {

                            lspos = stk[pos].fpos;

                            if (pos - lspos == 1) // 分支判断

                                   stk[lspos].bLeft = TRUE;

                            else

                                   stk[lspos].bRight = TRUE;

                            printf ("/r/n%02d.Pop(%d, %d)", pos, stk[pos].m, stk[pos].n);

                            --pos;

                     }

                     else

                     {

                            lspos = pos;

                            // push stack

                            printf ("/r/n%02d.Push(%d, %d)", pos, x - 1, y);

                            ++pos;

                            stk[pos].m = x - 1;

                            stk[pos].n = y;

                            stk[pos].bLeft = FALSE;

                            stk[pos].bRight = FALSE;

                            stk[pos].fpos = lspos;

 

                            printf ("/r/n%02d.Push(%d, %d)", pos, x, y - 1);

                            ++pos;

                            stk[pos].m = x;

                            stk[pos].n = y - 1;

                            stk[pos].bLeft = FALSE;

                            stk[pos].bRight = FALSE;

                            stk[pos].fpos = lspos;

                     }

              }

       }

 

       return res;

}

 

int main(int argc, char* argv[])

{

       int m = 5, n = 4, res = 0;

 

       DWORD tc1, tc2;

       tc1 = GetTickCount ();

       res = f(m, n);

       tc2 = GetTickCount ();

       printf ("%d : f(%d, %d) = %d/r/n", tc2 - tc1, m, n, res);

 

       tc1 = GetTickCount ();

       res = fs(m, n);

       tc2 = GetTickCount ();

       printf ("%d : f(%d, %d) = %d/r/n", tc2 - tc1, m, n, res);

 

       return 0;

}