reference binding to null pointer of type 'value_type'

Question

This is leetcode 26. Given a sorted array, remove the duplicates in-place such that each element appear only once and return the new length. An example is given nums = [1,1,2], the function should return [1,2].

Below is my code. I delete all the other duplicates, just leave one of them. However I always got an error of reference binding to null pointer of type 'value_type' when submitting. I would appreciate if anyone can help me with this!

class Solution { public:     int removeDuplicates(vector<int>& nums) {         int i = 0;         while(i < nums.size() - 1) {             if (nums[i] == nums[i + 1]) {                 nums.erase(nums.begin() + i);             }              else i++;         }         return nums.size();     } }; 

Answer 1

vector<T>::size() returns a value of type size_t, which is an unsigned type. Let's say the vector passed in is empty and therefore the vector's length is 0. nums.size() - 1 will cause integer underflow and you will actually be comparing 0 with a very large positive number. This will evaluate to true causing the loop to run and i going pass the array bounds.

To fix this you can cast nums.size() to int preemptively or store the size in an integer variable and compare with that.