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Last Updated: 8 Sep, 2020

# Pair Sum

Easy

## Problem statement

#### Note:

``````Each pair should be sorted i.e the first value should be less than or equals to the second value.

Return the list of pairs sorted in non-decreasing order of their first value. In case if two pairs have the same first value, the pair with a smaller second value should come first.
``````
##### Input Format:
``````The first line of input contains two space-separated integers 'N' and 'S', denoting the size of the input array and the value of 'S'.

The second and last line of input contains 'N' space-separated integers, denoting the elements of the input array: ARR[i] where 0 <= i < 'N'.
``````
##### Output Format:
``````Print 'C' lines, each line contains one pair i.e two space-separated integers, where 'C' denotes the count of pairs having sum equals to given value 'S'.
``````
##### Note:
``````You are not required to print the output, it has already been taken care of. Just implement the function.
``````
##### Constraints:
``````1 <= N <= 10^3
-10^5 <= ARR[i] <= 10^5
-2 * 10^5 <= S <= 2 * 10^5

Time Limit: 1 sec
``````

## Approaches

### 01 Approach

• Initialize a list to store our results.
• For each element in the array 'ARR[i]', check if ('ARR[i]' + ‘ARR[j]’), equals to given sum or not, where ‘i’ < ‘j’ < ‘N’.
• If the condition matches, add the pair('ARR[i]', ‘ARR[j]’) to the list. Sort the list of pairs as per the given output format and return this list.