Find Pairs with Sum

find_with_pairs_with_sum.js

function findPairsWithSum(arr, target) {
  // to store paris
  const pairs = [];
  // to store seen number with their index
  const seenNum = {};

  for (let i = 0; i < arr.length; i++) {
    // calculate the complement / pair by deducting the current number with target
    const complement = target - arr[i];

    // to prevent duplicate 
    // if complement seen then add it to pairs
    if(seenNum[complement] !== undefined){
      pairs.push([arr[i], complement])
    }

    seenNum[arr[i]] = i
  }
  return pairs;
}

const testCases = [
  {
    arr: [2, 7, 4, 0, 9, 5, 1, 3],
    target: 7,
    expected_length: 3
  },
  {
    arr: [0, 0, 0, 0, 0, 0, 0, 0],
    target: 7,
    expected_length: 0
  },
  {
    arr: [2, 7, 4, 0, 9, 5, 1, 3],
    target: 10,
    expected_length: 2
  },
]

testCases.forEach(({arr, target, expected_length}) => {
  const result = findPairsWithSum(arr, target)
  console.log(result)
  console.log(result.length === expected_length)
})