二叉树未理解部分

1. 求先序排列

#include <cstdio>
#include <cstring>

char in_order[10],post_order[10];
int len;

void read() {
    scanf("%s%s",in_order+1,post_order+1);
    len=strlen(in_order+1);
}

void bulid(int L1,int R1,int L2,int R2) {
    if(L1 > R1) {
        return ;
    }
    printf("%c",post_order[R2]);
    char Root=post_order[R2];
    int root_place=L1;
    while(in_order[root_place] != Root) {
        root_place++;
    }
    int cnt=root_place-L1;
    bulid(L1,root_place-1,L2,L2+cnt-1);
    bulid(root_place+1,R1,L2+cnt,R2-1);
}

int main(void) {
    read();
    bulid(1,len,1,len);
    return 0;
}

2. 遍历问题