93 复原IP地址

golang

func restoreIpAddresses(s string) []string {
	res := make([]string, 0)
	if len(s) < 4 || len(s) > 12 {
		return res
	}
	recursion(&res, "", s, 0)
	return res
}

func isValid(s string) bool {
	val, _ := strconv.Atoi(s)
	return val >= 0 && val <= 255 && (len(s) == 1 || s[0] != '0')
}

func recursion(res *[]string, s string, t string, k int) {
	fmt.Println(s, t)
	if k == 3 {
		if isValid(t) {
			*res = append(*res, s+t)
		}
	} else {
		for i := 1; i < 4 && i < len(t); i++ {
			tmp := t[:i]
			nxt := t[i:]
			//如果后面数位不可能组成正确ip地址就跳过以减少递归次数
			if isValid(tmp) && len(nxt) <= (3-k)*3 && len(nxt) >= 3-k {
				recursion(res, s+tmp+".", nxt, k+1)
			}
		}
	}
}