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
public class Solution {
public int NumIdenticalPairs(int[] nums) {
int count = 0;
var map = new Dictionary<int,int>();
for(int i=0;i<nums.Length;i++){
if(map.ContainsKey(nums[i])){
count+=map[nums[i]];
map[nums[i]]++;
}
else{
map.Add(nums[i],1);
}
}
return count;
}
}Time Complexity: O(n)
Space Complexity: O(n)
