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class Solution {
public:
    bool isStrobogrammatic(string num) {
        unordered_map<int, int> m;
        int n = num.size();
        m[1] = 1; m[0] = 0, m[6] = 9, m[8] = 8, m[9] = 6;

        for(int i=0, j=n-1; i<=j; i++, j--){
            int d = num[i]-'0';
            int d1 = num[j]-'0';
            if(!m.count(d) || m[d] != d1) return false;
        }
        return true;
    }
};