bfs代码：

#include <bits/stdc++.h>
using namespace std;

// 定义 BFS 函数
int bfs(const string &start_str, const vector<pair<int, int>> &rule) {
    int cnt = 1; // 初始化计数器
    int len = start_str.size();
    queue<string> q;
    unordered_set<string> vised; // 存储已经访问过的字符串

    q.push(start_str);
    vised.insert(start_str);

    while (!q.empty()) {
        string node = q.front();
        q.pop();
        for (auto &rr : rule) {
            char from = rr.first + '0';
            char to = rr.second + '0';
            for (int i = 0; i < len; i++) {
                if (node[i] == from) {
                    string new_node = node;
                    new_node[i] = to;
                    if (vised.find(new_node) == vised.end()) {
                        q.push(new_node);
                        vised.insert(new_node);
                        cnt++;
                    }
                }
            }
        }
    }
    return cnt;
}

int main() {
    string str;
    cin >> str;
    int k;
    cin >> k;
    vector<pair<int, int>> rule(k);
    for (int i = 0; i < k; i++) {
        cin >> rule[i].first >> rule[i].second;
    }
    int cnt = bfs(str, rule); // 调用 BFS 函数
    cout << cnt;
    return 0;
}

100分代码：

#include <bits/stdc++.h>
using namespace std;
int main() {
    string s;
    int k;
    // 输入初始数字
    cin >> s;
    int len = s.size();
    // 输入转换规则
    cin >> k;
    vector<pair<int, int>> rules(k);
    for (int i = 0; i < k; i++) {
        cin >> rules[i].first >> rules[i].second;
    }
    // 使用队列和集合
    queue<string> q;
    unordered_set<int> visited;

    // 初始化队列和访问集合
    q.push(s);
    visited.insert(stoi(s));
    int cnt = 1; // 初始包含原数
    // 广度优先搜索
    while (!q.empty()) {
        string current = q.front();
        q.pop();
        for (const auto &rule : rules) {
            char from = rule.first + '0';
            char to = rule.second + '0';

            // 对当前数字的每个字符进行尝试替换
            for (int i = 0; i < len; i++) {
                if (current[i] == from) {
                    string next = current;
                    next[i] = to;
                    int next_val = stoi(next);
                    if (visited.find(next_val) == visited.end()) {
                        visited.insert(next_val);
                        q.push(next);
                        cnt++;
                    }
                }
            }
        }
    }
    // 输出不同整数的个数
    cout << cnt << endl;
    return 0;
}