剑指 Offer 53-I. 在排序数组中查找数字 I

题目

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

提示:

  • 0 <= nums.length <= 105
  • -109 <= nums[i]<= 109
  • nums是一个非递减数组
  • -109 <= target <= 109

注意: 本题与主站34题相同(仅返回值不同)

题解

public int search(int[] nums, int target) {
    // 二分查找
    BiFunction<Integer, Integer, Integer> binarySearch = new BiFunction<Integer, Integer, Integer>() {
        @Override
        public Integer apply(Integer start, Integer end) {
            if (start > end || nums[end] < target || nums[start] > target) {
                return 0;
            }

            if (nums[end] == target || nums[start] == target) {
                int count = 0;
                for (int i = start; i <= end; i++) {
                    count += nums[i] == target ? 1 : 0;
                }

                return count;
            }

            int mid = (start + end) >> 1;
            return this.apply(start, mid) + this.apply(mid + 1, end);
        }
    };

    return binarySearch.apply(0, nums.length - 1);
}