剑指offer 53 -I 在排序数组中查找数字

统计一个数字在排序数组中出现的次数。

示例 1:

输入: nums = [5,7,7,8,8,10], target = 8
输出: 2

示例 2:

输入: nums = [5,7,7,8,8,10], target = 6
输出: 0

限制：

0 <= 数组长度 <= 50000

二分查找

/**
 * 二分查找
 *
 * @param nums
 * @param target
 * @return
 */
public static int search(int[] nums, int target) {
    if (nums == null || nums.length == 0) return 0;

    int cnt = 0;
    int left = 0, right = nums.length - 1;
    int mid = left;
    while (left <= right) {
        mid = (left + right) >> 1;
        if (nums[mid] == target) break;
        else if (nums[mid] > target) {
            right = mid - 1;
        } else {
            left = mid + 1;
        }
    }
    int index = mid;
    // 左侧
    while (index >= 0 && index < nums.length && nums[index] == target) {
        cnt++;
        index--;
    }
    index = mid + 1;
    // 右侧
    while (index >= 0 && index < nums.length && nums[index] == target) {
        cnt++;
        index++;
    }
    return cnt;
}

测试用例

public static void main(String[] args) {
    int[] nums = new int[]{0};
    int target = 0;
    int cnt = SearchSecond.search(nums, target);
    System.out.println("SearchSecond demo01 result : " + cnt);

    nums = new int[]{5, 7, 7, 8, 8, 10};
    target = 8;
    cnt = SearchSecond.search(nums, target);
    System.out.println("SearchSecond demo02 result : " + cnt);

    nums = new int[]{5, 7, 7, 8, 8, 10};
    target = 6;
    cnt = SearchSecond.search(nums, target);
    System.out.println("SearchSecond demo03 result : " + cnt);

    nums = new int[]{1, 2, 3, 3, 3, 3, 4, 5, 9};
    target = 3;
    cnt = SearchSecond.search(nums, target);
    System.out.println("SearchSecond demo04 result : " + cnt);

    nums = new int[]{1, 2, 3};
    target = 1;
    cnt = SearchSecond.search(nums, target);
    System.out.println("SearchSecond demo05 result : " + cnt);
}

运行结果