# 1980. Find Unique Binary String

Medium
Given an array of strings `nums` containing `n` unique binary strings each of length `n`, return a binary string of length `n` that does not appear in `nums`. If there are multiple answers, you may return any of them.
Example 1:
Input: nums = ["01","10"]
Output: "11"
Explanation: "11" does not appear in nums. "00" would also be correct.
Example 2:
Input: nums = ["00","01"]
Output: "11"
Explanation: "11" does not appear in nums. "10" would also be correct.
Example 3:
Input: nums = ["111","011","001"]
Output: "101"
Explanation: "101" does not appear in nums. "000", "010", "100", and "110" would also be correct.
Constraints:
• `n == nums.length`
• `1 <= n <= 16`
• `nums[i].length == n`
• `nums[i] `is either `'0'` or `'1'`.
• All the strings of `nums` are unique.

### 解題

func findDifferentBinaryString(nums []string) string {
m := make(map[int]bool)
for _, num := range nums {
if i, err := strconv.ParseInt(num, 2, 64); err == nil {
m[int(i)] = true // 紀錄有出現的數字
}
}
str := ""
ran := int(math.Pow(float64(2), float64(len(nums)))) // 範圍 : 0~2^len(nums)
for i := 0; i < ran; i++ {
if !m[i] { //一發現沒有出現過的，那就是答案
str = strconv.FormatInt(int64(i), 2)
break
}
}
return strings.Repeat("0", len(nums) - len(str)) + str //前面要補零
}