[刷题] PTA 03-树3 Tree Traversals Again

用栈实现树遍历

 1 #include<stdio.h>
 2 #include<string.h>
 3 #define MAXSIZE 30
 4
 5 int Pre[MAXSIZE],In[MAXSIZE],Post[MAXSIZE];
 6 void solve(int preL,int inL,int postL,int n);
 7 void outPut(int p[],int n);
 8
 9 int main(){
10     int n,tmp,i,j = 0;
11     int topPre = -1;
12     int topIn = -1;
13     const char *push = "Push";
14     char cnt[5];
15     int st[MAXSIZE];
16     scanf("%d",&n);
17     for(i=0; i<2*n; i++){
18         scanf("\n%s",cnt);
19         if(!strcmp(cnt,push)){
20             scanf("%d",&tmp);
21             Pre[j++] = tmp;
22             st[++topPre] = tmp;
23         }else{
24             In[++topIn] = st[topPre--];
25         }
26     }
27     solve(0,0,0,n);
28     outPut(Post,n);
29     return 0;
30 }
31
32 void solve(int preL, int intL, int postL, int n){
33     int i,L,R,root;
34     if(n==0) return;
35     if(n==1) {Post[postL] = Pre[preL]; return;}
36     root = Pre[preL];
37     Post[postL+n-1] = root;
38     for(i=0; i<n; i++) if(In[intL+i]==root) break;
39     L = i;R = n-L-1;
40     solve(preL+1, intL, postL, L);
41     solve(preL+L+1, intL+L+1, postL+L, R);
42 }
43
44 void outPut(int p[],int n){
45     int i;
46     for(i=0; i<n; i++){
47         if(!i) printf("%d",p[i]);
48         else printf(" %d",p[i]);
49     }
50 }

分析：

1、定义全局数组，Pre是对应先序遍历的输入，In是对应中序遍历的出栈，Post是对应后序遍历的输出

2、处理输入的过程用了栈的思路

3、solve()用了分治