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LeetCode.在排序数组中查找元素的第一个和最后一个位置

发表于 分类于 Valine：

给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。你的算法时间复杂度必须是 O(log n) 级别。如果数组中不存在目标值，返回 [-1, -1]。

  • 示例1:
    输入: nums = [5,7,7,8,8,10], target = 8
    输出: [3,4]
  • 示例2:
    输入: nums = [5,7,7,8,8,10], target = 6
    输出: [-1,-1]

解法:递归分治

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object BinarySearchRange {
     def main(args: Array[String]): Unit = {
          println(util.Arrays.toString(searchRange(Array(1, 2, 3, 3, 3, 4, 5), 3)))
          println(util.Arrays.toString(searchRange(Array(3, 4, 5), 3)))
          println(util.Arrays.toString(searchRange(Array(1, 2, 3, 3, 3, 4, 5), 3)))
          println(util.Arrays.toString(searchRange(Array(1, 2, 3, 4, 5), 3)))
          println(util.Arrays.toString(searchRange(Array(1, 2, 3, 4, 5), 1)))
          println(util.Arrays.toString(searchRange(Array(1, 2, 3, 4, 5), 5)))
          println(util.Arrays.toString(searchRange(Array(1, 2), 1)))
          println(util.Arrays.toString(searchRange(Array(1, 2), 2)))
          println(util.Arrays.toString(searchRange(Array(1, 1, 1, 1, 1, 1, 2, 3, 4, 4, 5, 5, 5, 6, 7, 8, 8, 8, 8), 8)))
          println(util.Arrays.toString(searchRange(Array(8, 8, 8, 8), 8)))
     }

     def searchRange(nums: Array[Int], target: Int): Array[Int] = {
          search(nums, 0, target)
     }

     def search(nums: Array[Int], index: Int, target: Int): Array[Int] = {
          if (nums.length == 0) return Array(-1, -1)
          if (nums.length == 1 && nums(0) == target) 0 else -1

          var l = 0
          var r = nums.length - 1

          val list = new Array[Int](2)

          while (l <= r) {
               val m = (l + r) / 2
               if (nums(m) > target) {
                    r = m - 1
               } else if (nums(m) < target) {
                    l = m + 1
               } else {
                    list(0) = m + index
                    list(1) = m + index
                    val left = search(nums.splitAt(m)._1, 0, target)
                    val right = search(nums.splitAt(m + 1)._2, m + index + 1, target)

                    if (left(0) != -1) {
                         list(0) = Math.min(left(0), list(0))
                    }

                    if (right(0) != -1) {
                         list(1) = Math.max(right(1), list(1))
                    }

                    return list
               }
          }

          Array(-1, -1)
     }
}