RT.
调了一天了。
做法与第一篇题解基本一致（我就是看的这篇题解）

#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e3 + 5;
struct Tree
{
    int ls, rs;
} givtree[maxn], mertree[maxn];
char givenstr[maxn];
int node_cnt = 0;
int id = 0;
int build()
{
    id++;
    int nowid=id;
    int now = ++node_cnt;
    if (givenstr[nowid] == '1' || givenstr[nowid] == '3')
    {
        givtree[now].ls = build();
    }
        
    if (givenstr[nowid] == '2' || givenstr[nowid] == '3')
    {
        givtree[now].rs = build();
    
    }
        
    
    return now;
}
char order[maxn];
int ordertop;
int find_node(int now)
{
    for (int i = 1; i <= ordertop; i++)
    {
        if (order[i] == 'L')
        {
            now = givtree[now].ls;
        }
        else
        {
            now = givtree[now].rs;
        }
    }
    return now;
}
int nodecnt2 = 1;
void merge(int givnow, int mernow, int exce)
{
    if(givnow==exce)return;
    if (givtree[givnow].ls)
    {
        if (!mertree[mernow].ls)
        {
            mertree[mernow].ls = ++nodecnt2;
        }
            
        //    printf("into 1\n");
        //     printf("ls: %d\n",mertree[mernow].ls);
        merge(givtree[givnow].ls, mertree[mernow].ls, exce);
    }
    if (givtree[givnow].rs)
    {
        if (!mertree[mernow].rs)
        {
            mertree[mernow].rs = ++nodecnt2;
        }
            
        //  printf("into 2\n");
        merge(givtree[givnow].rs, mertree[mernow].rs, exce);
    }
}
int calc()
{
    int now = 1, last = 0;
    while (now)
    {
  //      printf("calc now: %d\n", now);
        last = now;
        now = find_node(now);
        if(!now)break;
        merge(last, 1, now);
    }
    return nodecnt2;
}
int ans = 1e9;
void find_ans(int now, int dep)
{
    if (!now)
        return;
    if (now != 1)
    {
        nodecnt2 = 1;
        memset(mertree, 0, sizeof mertree);
        ans = min(ans, 2 * (calc()-1) - dep);
    }

    order[++ordertop] = 'L';
    find_ans(givtree[now].ls, dep + 1);
    order[ordertop] = 'R';
    find_ans(givtree[now].rs, dep + 1);
    ordertop--;
}
int main()
{
    scanf("%s", givenstr + 1);
    int n = strlen(givenstr + 1);
    build();
    find_ans(1, 0);
    printf("%d", ans);
    return 0;
}