// Package q401 implements a solution for https://leetcode.com/problems/binary-watch/
package q401

import "fmt"

func bin2time(leds []uint8) (string, bool) {
	hour := leds[0]<<3 + leds[1]<<2 + leds[2]<<1 + leds[3]
	minute := leds[4]<<5 +
		leds[5]<<4 +
		leds[6]<<3 +
		leds[7]<<2 +
		leds[8]<<1 +
		leds[9]
	if hour >= 12 || minute >= 60 {
		return "", false
	}
	return fmt.Sprintf("%d:%02d", hour, minute), true
}

func iterate(remaining, offset int, leds []uint8, ret *[]string) {
	if 10-offset < remaining {
		return
	}
	if remaining == 0 {
		if r, ok := bin2time(leds); ok {
			*ret = append(*ret, r)
		}
		return
	}

	leds[offset] = 1
	iterate(remaining-1, offset+1, leds, ret)
	leds[offset] = 0
	iterate(remaining, offset+1, leds, ret)
}

func readBinaryWatch(turnedOn int) []string {
	if turnedOn >= 9 {
		return nil
	}
	ret := []string{}
	iterate(turnedOn, 0, make([]uint8, 10), &ret)
	return ret
}

var _ = readBinaryWatch