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138 lines
4.1 KiB
Markdown
Executable File
138 lines
4.1 KiB
Markdown
Executable File
# [401. Binary Watch](https://leetcode.com/problems/binary-watch/)
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## 题目
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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**).
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Each LED represents a zero or one, with the least significant bit on the right.
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For example, the above binary watch reads "3:25".
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Given a non-negative integer n which represents the number of LEDs that are currently on, return all possible times the watch could represent.
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**Example**:
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Input: n = 1
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Return: ["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"]
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**Note**:
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- The order of output does not matter.
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- The hour must not contain a leading zero, for example "01:00" is not valid, it should be "1:00".
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- The minute must be consist of two digits and may contain a leading zero, for example "10:2" is not valid, it should be "10:02".
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## 题目大意
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二进制手表顶部有 4 个 LED 代表小时（0-11），底部的 6 个 LED 代表分钟（0-59）。每个 LED 代表一个 0 或 1，最低位在右侧。
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给定一个非负整数 n 代表当前 LED 亮着的数量，返回二进制表所有可能的时间。
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## 解题思路
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- 给出数字 n，要求输出二进制表中所有可能的时间
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- 题目中比较坑的是，分钟大于 60 的都不应该打印出来，小时大于 12 的也不应该打印出来，因为是非法的。给出的 num 大于 8 的也是非法值，最终结果应该输出空字符串数组。
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- 这道题的数据量不大，可以直接用打表法，具体打表函数见 `findReadBinaryWatchMinute()` 和 `findReadBinaryWatchHour()` 这两个函数。
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## 代码
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```go
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package leetcode
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import (
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"fmt"
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"strconv"
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)
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var (
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hour = []string{"1", "2", "4", "8"}
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minute = []string{"01", "02", "04", "08", "16", "32"}
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hourMap = map[int][]string{
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0: []string{"0"},
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1: []string{"1", "2", "4", "8"},
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2: []string{"3", "5", "9", "6", "10"},
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3: []string{"7", "11"},
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}
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minuteMap = map[int][]string{
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0: []string{"00"},
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1: []string{"01", "02", "04", "08", "16", "32"},
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2: []string{"03", "05", "09", "17", "33", "06", "10", "18", "34", "12", "20", "36", "24", "40", "48"},
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3: []string{"07", "11", "19", "35", "13", "21", "37", "25", "41", "49", "14", "22", "38", "26", "42", "50", "28", "44", "52", "56"},
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4: []string{"15", "23", "39", "27", "43", "51", "29", "45", "53", "57", "30", "46", "54", "58"},
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5: []string{"31", "47", "55", "59"},
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}
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)
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func readBinaryWatch(num int) []string {
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if num > 8 {
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return []string{}
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}
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res := []string{}
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for i := 0; i <= num; i++ {
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for j := 0; j < len(hourMap[i]); j++ {
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for k := 0; k < len(minuteMap[num-i]); k++ {
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res = append(res, hourMap[i][j]+":"+minuteMap[num-i][k])
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}
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}
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}
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return res
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}
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/// ---------------------------------------
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/// ---------------------------------------
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/// ---------------------------------------
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/// ---------------------------------------
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/// ---------------------------------------
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// 以下是打表用到的函数
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// 调用 findReadBinaryWatchMinute(num, 0, c, &res) 打表
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func findReadBinaryWatchMinute(target, index int, c []int, res *[]string) {
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if target == 0 {
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str, tmp := "", 0
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for i := 0; i < len(c); i++ {
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t, _ := strconv.Atoi(minute[c[i]])
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tmp += t
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}
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if tmp < 10 {
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str = "0" + strconv.Itoa(tmp)
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} else {
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str = strconv.Itoa(tmp)
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}
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// fmt.Printf("找到解了 c = %v str = %v\n", c, str)
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fmt.Printf("\"%v\", ", str)
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return
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}
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for i := index; i < 6; i++ {
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c = append(c, i)
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findReadBinaryWatchMinute(target-1, i+1, c, res)
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c = c[:len(c)-1]
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}
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}
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// 调用 findReadBinaryWatchHour(num, 0, c, &res) 打表
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func findReadBinaryWatchHour(target, index int, c []int, res *[]string) {
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if target == 0 {
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str, tmp := "", 0
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for i := 0; i < len(c); i++ {
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t, _ := strconv.Atoi(hour[c[i]])
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tmp += t
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}
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str = strconv.Itoa(tmp)
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//fmt.Printf("找到解了 c = %v str = %v\n", c, str)
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fmt.Printf("\"%v\", ", str)
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return
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}
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for i := index; i < 4; i++ {
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c = append(c, i)
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findReadBinaryWatchHour(target-1, i+1, c, res)
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c = c[:len(c)-1]
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}
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}
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``` |