size() return unsigned int --- record a stupid mistake

CPP
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One notification about .size() in c++

Today I made a stupid mistake when doing leetcode exercises… Just a record to avoid falling into the pit again…

The problem is:

1673. Find the Most Competitive Subsequence

Given an integer array nums and a positive integer k, return the most competitive subsequence of nums of size k.

An array’s subsequence is a resulting sequence obtained by erasing some (possibly zero) elements from the array.

We define that a subsequence a is more competitive than a subsequence b (of the same length) if in the first position where a and b differ, subsequence a has a number less than the corresponding number in b. For example, [1,3,4] is more competitive than [1,3,5] because the first position they differ is at the final number, and 4 is less than 5.

It an interesting problem, we need to put a less number to front as far as possible, and in the mean time, you should pay attention to the length of the results. A classic monotonic queue/stack problem, and the answer is simple:

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class Solution {
public:
    vector<int> mostCompetitive(vector<int>& nums, int k) {
        vector<int> ans;
        for (int i=0; i<nums.size(); ++i) {
            while (!ans.empty() && (ans.back() > nums[i]) && ans.size() + nums.size()-i-1 >= k) {
                ans.pop_back();
            }
            ans.push_back(nums[i]);
        }

        while (ans.size() > k) ans.pop_back();

        return ans;
    }
};

But you know what mistake I made? I wrote the while condition as:

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while (!ans.empty() && (ans.back() > nums[i]) && nums.size()-i-1 >= k - ans.size())

Seems no problem. However, since ans.size() is unsigned int, and k is a signed int. So what happens? k is converted to unsigned int. Whoops!