problem solving-3

//call stack
//recursion
//reduce

//stack data structure
// coin stack
// ball stack
//LIFO (Last In First out)
//Ball 4
//Ball 3
//Ball 2
//Ball 1

//Queue (data structure )
//(cash counter) 1 -  2 - 3 -4 - 5 - 6
// First In First Out(FIFo)

function three() {
  console.log(3)
}

function two() {
  three()
  console.log(2)
}

function one() {
  two()
  console.log(1)
}

one()

//factorial 5! = 5 * 4 * 3 * 2 * 1
//0! = 1

//recursion

// function factorial(num) {
//   let result = 1
//   if (num === 0) {
//     return result
//   }
//   for (let i = num; i >= 1; i--) {
//     result *= i
//     console.log(i)
//   }
//   console.log(result)
// }

// console.log(factorial(10))

// 5 * 4 * 3 * 2 * 1

// function factorial(num) {
//   //ending condition (base case)
//   if (num === 0) {
//     return 1
//   }
//   console.log(num)
//   return num * factorial(num - 1)
// }
// console.log(factorial(5))

// 5 *factorial(4)
// 4 * fact(3)

//1 * fact(1)

//1  * 1 * 2 * 3 * 4 * 5 = 120
//5 * 4 * 3 * 2 * 1 * 1   = 120

// sum of all values
//reduce (mandatory)

//1 + 2 = 3
//3 + 3 =  6
//6 + 4 =  10
//10 + 6 =  16

//10 + 1 = 11
//11 + 2 = 13
//13 + 3 = 16
//16 + 4 = 20
//20 + 6 = 26
// function sum(arr) {
//   return arr.reduce((acc, currentNum) => {
//     console.log(acc)
//     console.log(currentNum)
//     return (acc += currentNum)
//   }, 10)
// }

// console.log(sum([1, 2, 3, 4, 6]))
// let arr = [{ x: 1 }, { x: 2 }, { x: 3 }]

// function sum(inputArr) {
//   return inputArr.reduce(
//     (acc, currentValue) => {
//       console.log(currentValue)
//       acc.total += currentValue.x
//       console.log(acc)
//       return acc
//     },
//     {
//       total: 0,
//     }
//   )
// }
// console.log(sum(arr))

// let flattened = [
//   [0, 1],
//   [2, 3],
//   [4, 5],
// ].reduce(function (previousValue, currentValue) {
//   console.log(previousValue, currentValue)
//   return previousValue.concat(currentValue)
// }, [])

// let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice']

// let countedNames = names.reduce(function (allNames, name) {
//   // console.log(allNames)
//   // console.log(name)
//   if (name in allNames) {
//     allNames[name]++
//   } else {
//     allNames[name] = 1
//   }
//   return allNames
// }, {})

// console.log(countedNames)

// {
//     'Alice': 1
// }
// countedNames is:
// { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 }

let people = [
  { name: 'Alice', age: 21 },
  { name: 'Max', age: 20 },
  { name: 'Jane', age: 20 },
]

function groupBy(objectArray, property) {
  return objectArray.reduce(function (acc, obj) {
    console.log(obj)
    let key = obj[property]
    if (key in acc) {
      acc[key].push(obj)
    } else {
      acc[key] = [obj]
    }
    // console.log(acc)

    return acc
  }, {})
}

let groupedPeople = groupBy(people, 'age')

console.log(groupedPeople)
// groupedPeople is:
// {
//   20: [
//     { name: 'Max', age: 20 },
//     { name: 'Jane', age: 20 }
//   ],
//   21: [{ name: 'Alice', age: 21 }]
// }