求先序排列（简单

#include <iostream>
#include <set>
#include <vector>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <algorithm>
#define ll long long
using namespace std;
const int M = 1e3 + 1;
char pre[M];//代表后续
char in[M];//代表中序序列
inline void dfs(int root, int start, int end) {
    if (start >end) return ;
    cout << pre[root];
    int i;
    for (i = start; i <= end; i++) {
        if (pre[root] == in[i]) break;
    }
    dfs(root - (end - i + 1), start, i - 1);
    dfs(root - 1,i + 1, end);
    return ;
}
int main()
{
    scanf("%s", &in);
    getchar();
    scanf("%s", &pre);
    int len = strlen(pre);
//    cout<<len<<endl;
    dfs(len-1, 0, len - 1);
    return 0;
}