34. Search for a Range leetcode Python 2016 new season

hyperbolechi

于 2016-01-20 10:51:54 发布

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本文详细介绍了如何利用二分查找法在已排序的整数数组中找到指定目标值的起始和结束位置。通过实现`binSearch`和`searchRange`函数，我们可以高效地定位目标值，并返回其在数组中的区间。如果目标值不存在于数组中，则返回[-1, -1]。

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Given a sorted array of integers, find the starting and ending position of a given target value.

Your algorithm's runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

For example,
Given [5, 7, 7, 8, 8, 10] and target value 8,

return [3, 4].

1. do a binary search to check the position.

2. check both side until the number is no longer the target.

class Solution(object):
    def binSearch(self, nums, target):
        low = 0
        high = len(nums) - 1
        while True:
            if low > high:
                return -1
            mid = low + (high - low) / 2
            if nums[mid] < target:
                low = mid + 1
            elif nums[mid] > target:
                high = mid - 1
            else:
                return mid
    def searchRange(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        pos = self.binSearch(nums, target)
        if pos == -1:
            return [-1, -1]
        else:
            left, right = pos, pos
            while left >= 0 and nums[left] == target:
                left -= 1
            while right < len(nums) and nums[right] == target:
                right += 1
            return [left + 1, right - 1]