#7 코딩테스트 [소수 판별, 객체 정렬, Hash/객체]

1. 소수 판별

function isPrime(num) {
  if (num <= 1) return false;
  for (let i = 2; i <= parseInt(Math.sqrt(num)); i ++) {
    if (num % i === 0) return false;
  }
  return true;
}

https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Global_Objects/Math/sqrt

Math.sqrt() - JavaScript | MDN

 

2. 객체 정렬

https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

Array.prototype.sort() - JavaScript | MDN

let arr = [
    [6, 6],
    [2, 2],
    [4, 3],
    [4, 5],
    [10, 3]
];
let sortArr = arr.sort((a,b)=>(a[0]+a[1])-(b[0]+b[1]))

= arr.sort(function(a, b) {
  return (a[0] + a[1]) - (b[0] + b[1]);
});


[ [ 2, 2 ], [ 4, 3 ], [ 4, 5 ], [ 6, 6 ], [ 10, 3 ] ]

 

3. Hash

https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Global_Objects/Map/set

Map.prototype.set() - JavaScript | MDN

https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Global_Objects/Map/get

Map.prototype.get() - JavaScript | MDN

// 객체

function solution(s) {
    let answer;
    let max = 0;
    let stringHash = {};
    for (let ele of s) {
        if (!stringHash[ele]) {
            stringHash[ele] = 1;
        } else {
            stringHash[ele] += 1;
        }
    }
    for (let key in stringHash) {
        if (stringHash[key] >= max) {
            max = stringHash[key];
            answer = key;
        }
    }
    return answer;
}

{
  'B': 3,
  'A': 2,
  'C': 4,
  'D': 3,
  'E': 3
}

------------------------------------------------

// 해시

function solution(s) {
    let answer;
    let max = 0;
    let stringHash = new Map();
    for (let ele of s) {
        if (!stringHash.has(ele)) {
            stringHash.set(ele, 1)
        } else {
            stringHash.set(ele, stringHash.get(ele) + 1)
        }
    }
    for (let [key, value] of stringHash) {
        if (value >= max) {
            max = value
            answer = key
        }
    }
    return answer;
}

{
  'B' => 3,
  'A' => 2,
  'C' => 4,
  'D' => 3,
  'E' => 3
}