[刷题] PTA 03-树3 Tree Traversals Again

用栈实现树遍历

#include<stdio.h>
#include<string.h>
#define MAXSIZE 30

int Pre[MAXSIZE],In[MAXSIZE],Post[MAXSIZE];
void solve(int preL,int inL,int postL,int n);
void outPut(int p[],int n);

int main(){
    int n,tmp,i,j = 0;
    int topPre = -1;
    int topIn = -1;
    const char *push = "Push";
    char cnt[5];
    int st[MAXSIZE];
    scanf("%d",&n);
    for(i=0; i<2*n; i++){
        scanf("
%s",cnt);
        if(!strcmp(cnt,push)){
            scanf("%d",&tmp);
            Pre[j++] = tmp;
            st[++topPre] = tmp;            
        }else{
            In[++topIn] = st[topPre--];
        }
    }
    solve(0,0,0,n);
    outPut(Post,n);
    return 0;
}

void solve(int preL, int intL, int postL, int n){
    int i,L,R,root;
    if(n==0) return;
    if(n==1) {Post[postL] = Pre[preL]; return;}
    root = Pre[preL];
    Post[postL+n-1] = root;
    for(i=0; i<n; i++) if(In[intL+i]==root) break;
    L = i;R = n-L-1;
    solve(preL+1, intL, postL, L);
    solve(preL+L+1, intL+L+1, postL+L, R);
}

void outPut(int p[],int n){
    int i;
    for(i=0; i<n; i++){
        if(!i) printf("%d",p[i]);
        else printf(" %d",p[i]);
    }
}

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