search for a range

problem description:

　　given a sorted aescend array,return the begining and ending position of the target num

　　i.e:

　　[1,2,3,8,8,9]

　　return [3,4]

　　of course, if you can not find the target in the array, just return [-1,-1]

solution 1:

　　you can use the binary search to find the first num which equal to target in the array,then use two index named i, j to find the max length

　　there is my python solution

class Solution(object):
    def searchRange(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        length = len(nums)
        low = 0 
        high = length - 1
        while low <= high:
            middle = (low+high)/2
            if nums[middle] == target:
                i = middle
                j = middle
                while i>0 or j<length-1:
                    if i>0 and nums[i-1] == target:
                        i -= 1
                    elif j<(length-1) and nums[j + 1] == target:
                        j += 1
                    else:
                        break
                return [i,j]
            elif nums[middle]<target:
                low = middle +1
            else:
                high = middle -1
        return [-1,-1]

solution 2:

there is another more clever solution which published in the leetcode discussion.

the main idea is that you should fisrt find the start position,and then find the ending position.when find the start position you should make the middle seems prefer the left through make middle = (low+high)/2;when find the ending position you should make the middle seems prefer the right through make middle = (low+high)/2 +1

there is the python solution:

 

class Solution(object):
    def searchRange(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        ret = [-1, -1]
        low = 0
        length = len(nums)
        high = length - 1
        if length == 0:
            return ret
        while low < high:
            middle = (low+high)/2
            if nums[middle] < target:
                low = middle +1
            else:
                high = middle
        if nums[low] != target:
            return ret
        else:
            ret[0] = low
        high = length -1
        while low < high:
            middle = (low +high)/2 +1
            if nums[middle] > target:
                high = middle -1
            else:
                low = middle
        ret[1] = high 
        return ret

 

finally, thanks to stellari bring out such a wonderful solution