[LeetCode] Search Insert Position

The basic idea is to use binary search: keep two pointers

l

and

r

for the current search range, then find the middle element

nums[mid]

in this range. If

nums[mid] < target

, we know

target

should at least be inserted after

nums[mid]

, so we update

l = mid + 1

. Otherwise, update

r = mid

.

The code is as follows. Note that we initialize

r = n

instead of

n - 1

, which easily handles the case that

target

needs to be inserted after all the elements of

nums

.

class Solution {
public:
int searchInsert(vector<int>& nums, int target) {
int n = nums.size(), l = 0, r = n;
while (l < r) {
int mid = (l + r) / 2;
if (nums[mid] < target) l = mid + 1;
else r = mid;
}
return l;
}
};

In fact, this is just the sub-routine

search

in Solution 2 of Stefan's post. Thank Stefan for posting such a nice article!

Well, the system

lower_bound

may also be used, which just takes 1 line :-)

class Solution {
public:
int searchInsert(vector<int>& nums, int target) {
return lower_bound(nums.begin(), nums.end(), target) - nums.begin();
}
};