Solution3.cpp

class Solution {
public:
    int minimumOperations(vector<int>& nums, int start, int goal) {
        unordered_map<int, int> m1;
        unordered_map<int, int> m2;
        m1[start] = 0;
        m2[goal] = 0;
        queue<int> q1{{start}};
        queue<int> q2{{goal}};
        while (!q1.empty() && !q2.empty()) {
            int t = q1.size() <= q2.size() ? extend(m1, m2, q1, nums) : extend(m2, m1, q2, nums);
            if (t != -1) return t;
        }
        return -1;
    }

    int extend(unordered_map<int, int>& m1, unordered_map<int, int>& m2, queue<int>& q, vector<int>& nums) {
        for (int i = q.size(); i > 0; --i) {
            int x = q.front();
            int step = m1[x];
            q.pop();
            for (int y : next(nums, x)) {
                if (m1.count(y)) continue;
                if (m2.count(y)) return step + 1 + m2[y];
                if (y >= 0 && y <= 1000) {
                    m1[y] = step + 1;
                    q.push(y);
                }
            }
        }
        return -1;
    }

    vector<int> next(vector<int>& nums, int x) {
        vector<int> res;
        for (int num : nums) {
            res.push_back(x + num);
            res.push_back(x - num);
            res.push_back(x ^ num);
        }
        return res;
    }
};