이것이 취업을 위한 코딩테스트다. Chapter07

import java.util.*;
public class main {
    public static void main(String[] args) {

        Solution s = new Solution();

        boolean[] a = s.Chap07Example01(5, new int[]{8,3,7,9,2}, 3, new int[]{5,7,9});//이진탐색
        for(boolean aa : a)
            System.out.print(aa + " ");
        System.out.println();
        boolean[] b = s.Chap07Example01_Guide01(5, new int[]{8,3,7,9,2}, 3, new int[]{5,7,9});//계수정렬
        for(boolean aa : b)
            System.out.print(aa + " ");
        System.out.println();
        boolean[] c = s.Chap07Example01_Guide02(5, new int[]{8,3,7,9,2}, 3, new int[]{5,7,9});//집합자료형
        for(boolean aa : c)
            System.out.print(aa + " ");
        System.out.println();
        System.out.println(s.Chap07Exmaple02(4,6,new int[]{19,15,10,17}));
    }
}
class Solution {


    public boolean[] Chap07Example01(int n, int[] stock, int m, int[] find) {
        boolean[] answer = new boolean[m];

        Arrays.sort(stock);

        for(int i = 0; i<m;++i) {
            int start = 0;
            int mid = stock.length/2;
            int end = stock.length-1;
            while(start <= end) {
                if(stock[mid] < find[i]) {
                    start = mid+1;
                    mid = (end+start)/2;
                }
                else if(stock[mid] > find[i]) {
                    end = mid-1;
                    mid = (end+start)/2;
                }
                else {
                    answer[i] = true;
                    break;
                }
            }
        }
        return answer;
    }
    public boolean[] Chap07Example01_Guide01(int n, int[] stock, int m, int[] find) {
        boolean[] answer= new boolean[m];

        int[] stocks = new int[1000001];
        for(int s : stock)
            stocks[s] = 1;
        for(int i = 0; i<m;++i) {
            if(stocks[find[i]] == 1)
                answer[i] = true;
        }

        return answer;
    }
    public boolean[] Chap07Example01_Guide02(int n, int[] stock, int m, int[] find) {
        boolean[] answer= new boolean[m];
        Set<Integer> set = new HashSet<>();
        for(int s: stock)
            set.add(s);
        for(int i = 0; i<m;++i) {
            if(set.contains(find[i]))
                answer[i] = true;
        }
        return answer;
    }
    public int Chap07Exmaple02(int n, int m, int[] ddeok) {
        int answer = 0;

        Arrays.sort(ddeok);
        int start = 0;
        int end = ddeok[ddeok.length - 1];
        int mid = (start + end) / 2;
        while(true) {
            int tmp = 0;
            for(int d: ddeok) {
                if(d > mid) {
                    tmp += d-mid;
                }
            }
            if(tmp == m) {
                answer = mid;
                break;
            }
            else if(tmp < m) {
                end = mid-1;
                mid = (start+end)/2;
            }
            else if(tmp > m) {
                start = mid+1;
                mid = (start+end)/2;
            }
        }
        return answer;
    }
}

개념은 쉽지만 자칫 실수하면 찾기 힘들다. 개념을 맞게 다 써놨음에도 뭔가 오류가 생겼어서 뭐가 문제였지 하고 쳐다보고 있었다.