Given an array of integers nums.
A pair (i,j) is called good if nums[i] == nums[j] and i < j.
Return the number of good pairs.

Example 1:

Input: nums = [1,2,3,1,1,3]
Output: 4
Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.
Example 2:

Input: nums = [1,1,1,1]
Output: 6
Explanation: Each pair in the array are good.
Example 3:

Input: nums = [1,2,3]
Output: 0
 

Constraints:

1 <= nums.length <= 100
1 <= nums[i] <= 100

class Solution {
public:
    int numIdenticalPairs(vector<int>& nums) {
        int res = 0;
        int count[101] = {0};
        for(auto num : nums)
        {
            res += count[num]++;
        }
        
        return res;
    }
};

运行结果：

Runtime: 0 ms, faster than 100.00% of C++ online submissions for Number of Good Pairs.
Memory Usage: 7.5 MB, less than 20.58% of C++ online submissions for Number of Good Pairs.