246. Strobogrammatic Number

A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).

Write a function to determine if a number is strobogrammatic. The number is represented as a string.

Example 1:

Input:  "69"
Output: true

Example 2:

Input:  "88"
Output: true

Example 3:

Input:  "962"
Output: false

bool isStrobogrammatic(string num) { // time: O(n); space: O(1)
    string rotate(10, ' ');
    rotate['0' - '0'] = '0';
    rotate['1' - '0'] = '1';
    rotate['6' - '0'] = '9';
    rotate['8' - '0'] = '8';
    rotate['9' - '0'] = '6';
    int l = 0, r = num.length() - 1;
    while (l <= r) {
        if (rotate[num[l] - '0'] != num[r]) return false;
        ++l, --r;
    }
    return true;
}

bool isStrobogrammatic(string num) { // time: O(n); space: O(1)
    const string pattern = "00 11 88 696";
    string search;
    for (int i = 0, j = num.length() - 1; i <= j; ++i, --j) {
        search.clear();
        search.push_back(num[i]);
        search.push_back(num[j]);
        if (pattern.find(search) == string::npos) return false;
    }
    return true;
}