RainforestQA Interview Question

findUniquePairsThatSumTo.js

const sampleData = [0, 1, 100, 99, 0, 10, 90, 30, 55, 50, 33, 49, 49, 55, 75, 51, 49, 50, 51, 50, 49, 51];

const findUniquePairsThatSumToA = (summedValue, data) => {
  const usedValues = new Map([]);

  return data.reduce((acc, dataValue) => {
    const matchingPairUsedCount = usedValues.get(summedValue - dataValue) || 0;
    const matchingPairUsed = usedValues.has(summedValue - dataValue);
    if (matchingPairUsed && matchingPairUsedCount === 1) acc.push([dataValue, summedValue - dataValue]);
    usedValues.set(summedValue - dataValue, matchingPairUsedCount + 1);
    return acc;
  }, []);
};

console.log(findUniquePairsThatSumToA(100, sampleData));


const findUniquePairsThatSumToB = (summedValue, data) => {
  const output = [];
  data = data.sort((a, b) => a - b);

  let leftIndex = 0;
  let rightIndex = data.length - 1;

  const valuePairsMatchSum = () =>
    data[leftIndex] + data[rightIndex] === summedValue;
  const valuePairsGreaterThanSum = () =>
    data[leftIndex] + data[rightIndex] > summedValue;
  const valuePairsLessThanSum = () =>
    data[leftIndex] + data[rightIndex] < summedValue;
  const addPairToOutput = () =>
    output.push([data[leftIndex], data[rightIndex]]);
  const moveLeftIndex = () => {
    const currentValue = data[leftIndex];
    while (currentValue === data[leftIndex]) leftIndex++;
  };
  const moveRightIndex = () => {
    const currentValue = data[rightIndex];
    while (currentValue === data[rightIndex]) rightIndex--;
  };
  const crunch = () => {
    if (leftIndex >= rightIndex) return output;
    
    if (valuePairsMatchSum()) {
      addPairToOutput();
      moveLeftIndex();
      moveRightIndex();
    }
    
    if (valuePairsLessThanSum()) moveLeftIndex();

    if (valuePairsGreaterThanSum()) moveRightIndex();

    crunch();
    return output;
  };

  return crunch();
}

console.log(findUniquePairsThatSumToB(100, sampleData));

In my previous revision utilizing a Set, I realized that having multiple duplicate numbers such as 3 50s would throw it off. Using a Map simplifies the logic and allows me to keep a count of which paired numbers I have already used.

Adding a fun way that only needs to walk through half of the array, but requires it to be sorted first.