Two Pointers

Pointers

1) Find two numbers in the sorted array sum of which are 0.

function sumZero(arr) {
    let left = 0;
    let right = arr.length - 1;
    while(left < right) {
        let sum = arr[left] + arr[right];
        if (sum === 0) return [arr[left], arr[right]];
        sum > 0 ? --right : ++left;
    }
}

console.log(sumZero([-4,-3,-2,-1,0,1,2,3,10])); // [-3, 3]
console.log(sumZero([-4,-3,-2,-1,0,6,7,8,10])); // undefined

2) Count the unique values in the sorted array.

function countUniqueValues(arr) {
  if (!arr.length) return 0
  let i = 0
  for (let j = 1; j < arr.length; j++) {
      if (arr[i] !== arr[j]) {
          i++;
          arr[i] = arr[j]
      }
  }
  return i + 1
}

console.log(countUniqueValues([1,1,1,1,2,3])); // 3