leet code 997. 找到小镇的法官

class Solution {
public:
    int findJudge(int N, vector<vector<int>>& trust) {
        if (N==0) {
            return -1;
        }
       
        if (trust.empty()) {
            if (N == 1) {
                return 1;
            }
            else {
                return -1;
            }
        }
        unordered_map<int, int> be_trusted_num;
        unordered_map<int, int> trust_num;

        for (const auto p:trust) {
            auto b_itr = be_trusted_num.find(p[1]);
            if (b_itr == be_trusted_num.end()) {
                be_trusted_num[p[1]] = 1;
            }
            else {
                b_itr->second++;
            }

            auto t_itr = trust_num.find(p[0]);
            if (t_itr == trust_num.end()) {
                trust_num[p[0]] = 1;
            }
            else {
                t_itr->second++;
            }
        }

        for (const auto bt:be_trusted_num) {
            if (bt.second == N-1) {
                auto t_itr = trust_num.find(bt.first);
                if (t_itr == trust_num.end()) {
                    return bt.first;
                }
            }
        }

        return -1;
    }
};