Java 코테 준비 [내가 기억하고 싶어서]

2D array에서 정렬

Arrays.sort(validData, Comparator.comparingInt(pair -> pair[1]));

글자 n개 쓰기

String hi = "hi";
String hihi = "hi".repeat(2);

String -> int

(int)X.charAt(i) - '0';

Sorting arrays & array lists

Arrays.sort(arr);
Arrays.sort(arr, Collections.reverseOrder());

Collections.sort(arrList);
Collections.reverse(arrList);

Initialize list of size n with same value

int[] arr = new int[n];
Arrays.fill(arr, -1);

ArrayList to Array

arrList.toArray();

10진법 -> 2진법

private int[] getBinary(int num, int size) {
    List<Integer> arr = new ArrayList<>();
    while (num > 0) {
        arr.add(0, num % 2);
        num /= 2;
    }
        
    int[] ans = new int[size];
        
    for (int i = 0; i < arr.size(); i++) {
        ans[size-1-i] = arr.get(arr.size()-i-1);
    }
        
    return ans;
}

Check if char is int

Character.isDigit(string.charAt(index));
Character.isLetter(string.charAt(index));