plusOne.js

// 66. Plus One

// You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0's.

// Increment the large integer by one and return the resulting array of digits.

 

// Example 1:

// Input: digits = [1,2,3]
// Output: [1,2,4]
// Explanation: The array represents the integer 123.
// Incrementing by one gives 123 + 1 = 124.
// Thus, the result should be [1,2,4].
// Example 2:

// Input: digits = [4,3,2,1]
// Output: [4,3,2,2]
// Explanation: The array represents the integer 4321.
// Incrementing by one gives 4321 + 1 = 4322.
// Thus, the result should be [4,3,2,2].
// Example 3:

// Input: digits = [9]
// Output: [1,0]
// Explanation: The array represents the integer 9.
// Incrementing by one gives 9 + 1 = 10.
// Thus, the result should be [1,0].

var plusOne = function(digits) {
    let response = []
    // This will only run if all the numbers in the digit is 9. 
    const areAllNine = digits.every(num => num === 9)
    if(areAllNine){
        const allZero = Array(digits.length).fill(0)
        response = [1,...allZero]
        return response
    }

    response = [...digits]
    let extraVal = 1
    for(let i = digits.length-1; i > -1; i--){
        const sum = digits[i] + extraVal
    // if the sum is equal to 10, then the last number will be 0
    // you are adding 1 to the number you are iterating through. 
        if(sum === 10){
            response[i] = 0
            extraVal = 1
    // fi the sum anything else, which is less than 10, then you are adding 0, and the number stays the same, b/c you are adding 0. 
        }else{
            extraVal = 0
            response[i] = sum
        }
    }
    return response
};