面试题56 - I. 数组中数字出现的次数

落日映苍穹つ 2023-07-24 09:03 41阅读 0赞

**往期回顾：**

\[1\]. [python中的collection模块][python_collection]  
\[2\]. [leetcode–137–只出现一次的数字 II (面试题56 - II. 数组中数字出现的次数 II)][leetcode_137_ II _56 - II. _ II]

**题目描述：**

一个整型数组 nums 里除两个数字之外，其他数字都出现了两次。请写程序找出这两个只出现一次的数字。

**示例 1：**

输入：nums = [4,1,4,6]
    输出：[1,6] 或 [6,1]

**示例 2：**

输入：nums = [1,2,10,4,1,4,3,3]
    输出：[2,10] 或 [10,2]

--------------------

**解题思路1:**

1.  利用Counter，首先进行频数统计，然后将每一项列出来，并转化成列表的形式
2.  依次遍历频数即可

--------------------

**代码1：**

from collections import Counter
    class Solution(object):
        def singleNumbers(self, nums):
            number = list(Counter(nums).items())
            ans = []
            for i in range(len(number)):
                if number[i][1] != 2:
                    ans.append(number[i][0])
            return ans
    
    s = Solution()
    nums = [4,1,4,6]
    print(s.singleNumbers(nums))

或者依次遍历键来找值

from collections import Counter
    class Solution:
        def singleNumbers(self, nums):
            hashmap = Counter(nums)
    
            ans = []
            for k in hashmap.keys():
                if hashmap[k] == 1:
                    ans.append(k)
            return ans

--------------------

**解题思路2:**

1.  遍历数据，用一个字典存储每个数字出现的次数
2.  依次找出字典中出现次数为1的数字

--------------------

**代码2：**

class Solution:
        def singleNumbers(self, nums):
            dt = {
        }
            for num in nums:
                if num not in dt:
                    dt[num] = 1     # num是键，dt[num]是值
                else:
                    dt[num] += 1
    
            ans = []
            for key in dt:
                if dt[key] == 1:
                    ans.append(key)
            return ans

--------------------

**参考链接:**

[leetcode–137–只出现一次的数字 II (面试题56 - II. 数组中数字出现的次数 II)][leetcode_137_ II _56 - II. _ II]

--------------------

**题目来源：**

[https://leetcode-cn.com/problems/shu-zu-zhong-shu-zi-chu-xian-][https_leetcode-cn.com_problems_shu-zu-zhong-shu-zi-chu-xian-]

--------------------

**拓展：**

统计一个数字在排序数组中出现的次数。

from collections import Counter
    class Solution:
        def GetNumberOfK(self, data, k):
            num = Counter(data)
            return num[k]
    
    
    s = Solution()
    data = [1,2,3,3,3,3,4,5]
    k = 3
    print(s.GetNumberOfK(data, k))

[python_collection]: https://blog.csdn.net/weixin_43283397/article/details/104967068
[leetcode_137_ II _56 - II. _ II]: https://blog.csdn.net/weixin_43283397/article/details/105305580
[https_leetcode-cn.com_problems_shu-zu-zhong-shu-zi-chu-xian-]: https://leetcode-cn.com/problems/shu-zu-zhong-shu-zi-chu-xian-