34. Search for a Range
欢迎fork and star:Nowcoder-Repository-github
34. Search for a Range
题目
Given an array of integers sorted in ascending order, 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].
解析
- 关于二分法的查找延伸的问题,细节要注意
- 注意使用stl的函数实现,在[first,last)区间查找
class Solution_34 {
public:
int findUpBound(vector<int>& nums, int target) //找上边界
{
int low = 0, high = nums.size() - 1;
if (nums.back()<target)
{
return -1;
}
while (low<=high)
{
int mid = (low + high) >> 1;
if (nums[mid]<=target) /// 向右夹逼,找到右边界
{
low = mid + 1;
}
else
{
high = mid - 1;
}
}
return high; //向右夹逼,返回high
}
int findDownBound(vector<int>& nums, int target) // 找下边界
{
int low = 0, high = nums.size() - 1;
if (nums.front()>target)
{
return -1;
}
while (low<=high)
{
int mid = (low + high) >> 1;
if (nums[mid]<target) /// 向左夹逼,则找到左边界
{
low = mid + 1;
}
else
{
high = mid - 1;
}
}
return low; // 向左夹逼,返回low
}
vector<int> searchRange(vector<int>& nums, int target) { //找到target的上下边界
vector<int> vec(2, -1);
if (nums.size() == 0 || nums.front()>target || nums.back()<target)
{
return vec;
}
int high = findUpBound(nums, target);
int low = findDownBound(nums, target);
if ((low == high&&nums[low] == target) || (low<high))
{
vec[0] = low;
vec[1] = high;
}
return vec;
}
vector<int> searchRange2(int A[], int n, int target) {
vector<int > vec(A,A+n); //初始化
return searchRange1(vec, target);
}
vector<int> searchRange1(vector<int>& nums, int target) { //找到target的自身上下边界,非严格上下界
vector<int> vec(2, -1);
if (nums.size() == 0||nums.front()>target||nums.back()<target)
{
return vec;
}
//pair<int, int> temp;
//针对 upper_bound the objects in the range [first,last) are accessed. 本身传入的迭代器end().就是指向下一个位置
auto range=equal_range(nums.begin(), nums.end(), target); //返回的是两个迭代器,解引用得到值
if (*range.first!=target||*(range.second-1)!=target)
{
return vec;
}
vec[0]=(range.first-nums.begin()); //stl: distance()计算迭代器之间的距离
vec[1]=(range.second - nums.begin()-1);
return vec;
}
};
题目来源
C/C++基本语法学习
STL
C++ primer