Questions-review-dictionary-closures.swift

import UIKit

// Questions review

// dictionary question

// given an array of integers write a function that returns a dictionary of
// occurences of each integer
// input: [1, 3, 1, 1, 3, 4, 1, 8, 2, 7, 8]
// output: [7: 1, 1: 4, 3: 2, 8: 2, 2: 1, 4: 1]
func occurencesOfInteger(arr: [Int]) -> [Int: Int] {
  var frequencyDictionary = [Int: Int]()
  for number in arr {
    // using optional binding to unwrap the value at the given key in our
    // frequencyDictionary
    // enter the if let statement if we have seen the number before and
    // increment count by 1
    if let count = frequencyDictionary[number] {
      frequencyDictionary[number] = count + 1
    } else {
      // first time visiting a number we want to set the count of
      // occurences to 1
      
      // appending of an element in the dictionary happens here
      
      // e.g first time
      // [:]
      frequencyDictionary[number] = 1
      
      // first adding the first element from the array our dictionary looks like below
      // [1: 2, 3: 2, 4: 1, 8: 2, 2: 1, 7: 1]
    }
  }
  return frequencyDictionary
}
let results = occurencesOfInteger(arr: [1, 3, 1, 1, 3, 4, 1, 8, 2, 7, 8])
print(results) // [4: 1, 2: 1, 3: 2, 1: 4, 7: 1, 8: 2] - will be unordered as is the definition of a dictionary



// closure question

// write a function called largestValue(in: ) that finds the largest Int in an array of Ints. Use reduce to
// solve this exercise.
func largestValue(in numbers: [Int]) -> Int {
  
  // using guard to ensure an array is not empty
  // guard numbers.count > 0 else { return -1 }
  
  // using guard to get the first element
  guard let first = numbers.first else { return -1 }
  
//  if let first = numbers.first {
//    // ONLY has access to first inside if let statement
//    print(first)
//  } else {
//    //first - DOES NOT COMPILE
//  }
  
  // using trailing closure syntax to solve reduce exercise
  let result = numbers.reduce(first) { prevResult, currentValue in
    if prevResult > currentValue {
      return prevResult
    } else {
      return currentValue
    }
  }
  // 1. numbers.reduce(0, +)
  /* 2. numbers.reduce(0) { prevResult, currentValue in
          // code here
        }
  */
  return result
}
let largestResult = largestValue(in: [56, 100, -56, 0, 208])
print(largestResult) // 208