LeetCode Q34: Search for a Range

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].

Straight forward solution. Binary search first followed by a local scanning around mid pointer.

	class Solution {
	public:
	int rBound(vector<int>& nums, int target, int l, int r){
	if(l>r)
	return -1;
	while(l<=r){
	int mid = (l+r)/2;
	if(target<nums[mid]){
	r=mid-1;
	continue;
	}
	if(target>nums[mid]){
	l=mid+1;
	continue;
	}
	if(target==nums[mid]){
	if((mid+1<nums.size() && nums[mid]!=nums[mid+1]) || (mid==nums.size()-1))
	return mid;
	else
	l=mid+1;
	}
	}
	return -1;
	}
	int lBound(vector<int>& nums, int target, int l, int r){
	if(l>r)
	return -1;
	while(l<=r){
	int mid = (l+r)/2;
	if(target<nums[mid]){
	r=mid-1;
	continue;
	}
	if(target>nums[mid]){
	l=mid+1;
	continue;
	}
	if(target==nums[mid]){
	if((mid-1>=0 && nums[mid]!=nums[mid-1]) || (mid==0))
	return mid;
	else
	r=mid-1;
	}
	}
	return -1;
	}
	vector<int> searchRange(vector<int>& nums, int target) {
	vector<int> res;
	if(nums.empty())
	return res;
	int lb = lBound(nums, target, 0, nums.size()-1);
	int rb = rBound(nums, target, 0, nums.size()-1);
	res.push_back(lb);
	res.push_back(rb);
	return res;
	}
	};

view raw Q34SearchforaRange.cpp hosted with ❤ by GitHub