Equivalent Pairs - Amazon Top Interview Questions


Problem Statement :


You are given a list of integers nums. Return the number of pairs i < j such that nums[i] = nums[j].

Constraints

0 ≤ n ≤ 100,000 where n is the length of nums

Example 1

Input
nums = [3, 2, 3, 2, 2]


Output
4


Explanation
We have index pairs (0, 2), (1, 3), (1, 4), (3, 4).


Solution :



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                        Solution in C++ :

int solve(vector<int>& nums) {
    unordered_map<int, int> m;
    int ans = 0;
    for (int i = 0; i < nums.size(); i++) {
        ans += m[nums[i]]++;
    }
    return ans;
}
                    


                        Solution in Java :

import java.util.*;

class Solution {
    public int solve(int[] nums) {
        Map<Integer, Integer> hm = new HashMap<>();
        int r = 0;
        for (int i = 0; i < nums.length; i++) {
            hm.put(nums[i], hm.getOrDefault(nums[i], 0) + 1);
            r = r + hm.get(nums[i]) - 1;
        }
        return r;
    }
}
                    


                        Solution in Python : 
                            
class Solution:
    def solve(self, nums):
        count = defaultdict(int)
        ans = 0
        for i in nums:
            ans += count[i]
            count[i] += 1
        return ans


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