leetcode——Search Insert Position

题目：

Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.

You may assume no duplicates in the array.

Here are few examples.

[1,3,5,6]

, 5 → 2

[1,3,5,6]

, 2 → 1

[1,3,5,6]

, 7 → 4

[1,3,5,6]

, 0 → 0

class Solution {
public:
int searchInsert(vector<int>& nums, int target) {
if (nums.empty())
{
return 0;
}
/*找到第一个大于等于target的位置，那么可能需要比较first和first-1的位置
因此,让first从1开始比较合理
*/
if (nums[0] >= target)
{
return 0;
}
//先比较最后一个元素，这样让last从nums.size()开始，防止越界
int first = 1, last = nums.size();
while (first < last)
{
if (nums[first] == target || (nums[first] > target && nums[first - 1] < target))
{
return first;
}

int mid = first + (last - first) / 2;

if (nums[mid] == target || (nums[mid] > target && nums[mid - 1] < target))
{
return mid;
}
else if (nums[mid] < target)
{
first = mid + 1;
}
else
{
last = mid;
}
}

//没有找到大于等于target的元素，那么返回nums.size()
return nums.size();
}
};