子序列与全排列

字符串子序列

func process1(str string, index int, ans *[]string, path string) {
	if index == len(str) {
		*ans = append(*ans, path)
		return
	}
	process1(str, index+1, ans, path)
	process1(str, index+1, ans, path+string(str[index]))
}

字符串去重子序列

func process2(str string, index int, ans map[string]struct{}, path string) {
	if index == len(str) {
		if _, ok := ans[path]; !ok {
			ans[path] = struct{}{}
		}
		return
	}
	process2(str, index+1, ans, path)
	process2(str, index+1, ans, path+string(str[index]))
}

字符串全排列

func process3(str []byte, index int, ans *[]string) {
	if index == len(str) {
		*ans = append(*ans, string(str))
	} else {
		for i := index; i < len(str); i++ {
			str[index], str[i] = str[i], str[index]
			process3(str, index+1, ans)
			str[i], str[index] = str[index], str[i]
		}
	}
}

字符串去重全排列

func process4(str []byte, index int, ans *[]string) {
	if index == len(str) {
		*ans = append(*ans, string(str))
	} else {
		visited := [256]bool{}
		for i := index; i < len(str); i++ {
			if visited[str[i]] {
				continue
			}
			visited[str[i]] = true
			str[index], str[i] = str[i], str[index]
			process4(str, index+1, ans)
			str[i], str[index] = str[index], str[i]
		}
	}
}