[leetcode] problem 401 – binary watch

A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).

Each LED represents a zero or one, with the least significant bit on the right.

For example, the above binary watch reads “3:25”.

Given a non-negative integer n which represents the number of LEDs that are currently on, return all possible times the watch could represent.

Example

Note

Code

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public List<String> (int num) {
    List<String> result = new ArrayList<>();

    for (int h = 0; h < 12; h++) {
        for (int m = 0; m < 60; m++) {
            if (Integer.bitCount((h << 6) + m) == num)
                result.add(h + ":" + (m < 10 ? "0" + m : m));;
        }
    }

    return result;
}