Taken from DailyCodingProblem

Given an array of integers, write a function to determine whether the array could become non-decreasing by modifying at most 1 element.

For example, given the array [10, 5, 7], you should return true, since we can modify the 10 into a 1 to make the array non-decreasing.

Given the array [10, 5, 1], you should return false, since we can’t modify any one element to get a non-decreasing array.

Solution

This is the answer I came up with:

function couldBeNonDecreasing(arr: Array<number>): boolean {
  // As long as the first element is larger than the second,
  // and the second larger than the third, always return false
  if (arr[0] > arr[1] && arr[1] > arr[2]) {
    return false
  }
    
  // Otherwise, return true
  return true
}

If at most one element can be changed, then the maximum array length is always 3. Also, non-decreasing means the array items are less than or equal to each other in ascending order, i.e. arr[0] <= arr[1] && arr[1] <= arr[2]

Testing

Solution tested in REPL:

https://www.typescriptlang.org/play?ssl=10&ssc=2&pln=1&pc=1#code/GYVwdgxgLglg9mABBOIA2ATAQgUwHIIAiOEATjgIYDOMYA5gBQWmkBciAgixQJ4A8YEAFsARjlIA+AJTsRcOGkpIA3gFgAUIkQB6bZyqI0COomqIoACxyJgMUlSiIcioTjCOYBtMzrjzFiiRLayoSBAwAGg0tXVMwDH8QsPjDHz9LQMT-O0jTNAB3XgNyKBBSJGAKNFDoxBhgRCYWAG0ABgBdRAlTFoBGToAyAZ7SZv6ukeaAJnapRDVNLUQSsoqqmsWAX1qtWtiAeWDSfM8cCOWcUvLzUhAcWpXrqFv79W31DRQwKgUcADojIxaih0Nh8EQSORqLRGGNWucAKznfpSc6xSrVV5aEGYXAEMDEMiUGj0BhwxHnADsszRemed0QzQALBTENTgahceCCZDiTCyb1WSjaTcGWNkYh+hzQXiIUToaTmgBOZEAZmRNJ0dJejJVkvVkqZ7WlXPxhKhJNhBsFiA6qK1NnWrykGiAA