코딩테스트 입문 - Day 22

저주의 숫자 3

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class Solution {
    public int solution(int n) {
        int tenc = 1;
        int thc = 1;
        while(tenc <= n){
            if(thc % 3 == 0){
                thc++; 
                continue;
            }
            else if(String.valueOf(thc).contains("3")){
                thc++;
                continue;
            }
            thc++;
            tenc++;
        }
        return thc - 1;
    }
}

평행

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class Solution {
    public int solution(int[][] dots) {
        return isParallel(dots[0], dots[1], dots[2], dots[3]) ||
               isParallel(dots[0], dots[2], dots[1], dots[3]) ||
               isParallel(dots[0], dots[3], dots[1], dots[2]) ? 1 : 0;
    }

    private boolean isParallel(int[] a, int[] b, int[] c, int[] d) {
        return (b[1] - a[1]) * (d[0] - c[0]) == (d[1] - c[1]) * (b[0] - a[0]);
    }
}

겹치는 선분의 길이

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import java.util.Arrays;
import java.util.Comparator;

class Solution {
     public static int solution(int[][] lines) {
        int answer = 0;

        Arrays.sort(lines, Comparator.comparingInt(o -> o[0]));
        int start_idx = lines[0][0];
        int end_idx = lines[0][1];

        for(int i = 1; i < lines.length; i++) {
            int curStart = Math.max(start_idx, lines[i][0]);
            int curEnd = Math.min(end_idx, lines[i][1]);

            if(curStart < curEnd){
                answer += curEnd - curStart;
                start_idx = curEnd;
                end_idx = Math.max(end_idx,lines[i][1]);
                continue;
            }
            start_idx = lines[i][0];
            end_idx = lines[i][1];
        }
        return answer;
    }
}

유한소수 판별하기

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class Solution {
    public int solution(int a, int b) {
        int gcd = getGCD(a, b);
        b /= gcd; 

        while (b % 2 == 0) b /= 2;
        while (b % 5 == 0) b /= 5;

        return b == 1 ? 1 : 2;
    }

    private int getGCD(int a, int b) {
        if (b == 0) return a;
        return getGCD(b, a % b);
    }
}