算法训练营day22, 回溯2
216. 组合总和 III
func combinationSum3(k int, n int) [][]int {
//存储全部集合
result := make([][]int, 0)
//存储单次集合
path := make([]int, 0)
var backtrace func(k int, n int, sum int, startIndex int)
backtrace = func(k int, n int, sum int, startIndex int) {
//当单次集合大小和k值相等，找到本次集合，但path需要一直使用需要用temp临时存储然后赋给result
if len(path) == k {
if sum == n {
temp := make([]int, k)
copy(temp, path)
result = append(result, temp)
return
}
}
for i := startIndex; i <= 9; i++ {
if sum+i > n { // 剪枝
break
}
sum += i
path = append(path, i)
backtrace(k, n, sum, i+1)
//回溯处理
sum -= i
path = path[:len(path)-1]
}
}
backtrace(k, n, 0, 1)
return result
}
17. 电话号码的字母组合
func letterCombinations(digits string) []string {
result := make([]string, 0)
if len(digits) == 0 {
return result
}
letterMap := make(map[int]string, 0)
letterMap[0] = ""
letterMap[1] = ""
letterMap[2] = "abc"
letterMap[3] = "def"
letterMap[4] = "ghi"
letterMap[5] = "jkl"
letterMap[6] = "mno"
letterMap[7] = "pqrs"
letterMap[8] = "tuv"
letterMap[9] = "wxyz"
//存储单次集合
path := make([]byte, 0)
var backtrace func(digits string, index int)
backtrace = func(digits string, index int) {
if index == len(digits) {
temp := string(path)
result = append(result, temp)
return
}
//转换为int
digit := int(digits[index] - '0')
letter := letterMap[digit]
for i := 0; i < len(letter); i++ {
path = append(path, letter[i])
backtrace(digits, index+1)
//回溯处理
path = path[:len(path)-1]
}
}
backtrace(digits, 0)
return result
}