789. 数的范围

789. 数的范围 - AcWing题库

Question

Content

Solution

Java

import java.util.Scanner;
import java.util.stream.IntStream;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int q = scanner.nextInt();

        int[] arr = IntStream.range(0, n)
                .map(i -> scanner.nextInt()).toArray();

        while (q-- > 0) {
            int k = scanner.nextInt();
            int[] ans = binarySearch(arr, k);
            IntStream.range(0, 2).mapToObj(i -> ans[i] + " ")
                    .forEach(System.out::print);
            System.out.println();
        }
    }

    private static int[] binarySearch(int[] arr, int target) {
        int[] ans = new int[]{-1, -1};
        int left = 0, right = arr.length - 1;
        int idx = leftBinarySearch(arr, left, right, target);
        if (arr[idx] != target) {
            return ans;
        }

        ans[0] = idx;
        idx = rightBinarySearch(arr, left, right, target);
        ans[1] = idx;

        return ans;
    }

    private static int leftBinarySearch(int[] arr, int left, int right, int target) {
        while (left < right) {
            int mid = (left + right) >> 1;
            if (arr[mid] >= target) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }

    private static int rightBinarySearch(int[] arr, int left, int right, int target) {
        while (left < right) {
            int mid = (left + right + 1) >> 1;
            if (arr[mid] <= target) {
                left = mid;
            } else {
                right = mid - 1;
            }
        }
        return left;
    }

}