Why stoi() function is not working in the following code?

Question

class Solution {
public:
    string kthLargestNumber(vector<string>& nums, int k) {
        priority_queue<int>q;
        for(int i=0;i<nums.size();i++)
        {
            q.push(stoi(nums[i]));
        }
        while(!q.empty())
        {
                k--;
                if(k==0)
                {
                    return q.top();
                }
                q.pop();
        }
        return 0;   
    }
};

I was trying to solve Leetcode 1985. Find the Kth Largest Integer in the Array problem. But I am having a Compile Error at line no 14 ( return q.top(); ) I don't know why this happening.

Problem Link

When asking questions about build errors, then please always copy-paste (as text!) the full and complete error output into the question. — Some programmer dude, Mar 25 '23 at 10:43
As a hint: What does `q.pop()` *return*? And why would you want to return an `int` in a function declared to return a `string`? — Some programmer dude, Mar 25 '23 at 10:43
@Someprogrammerdude It seems that you did not even click on the provided link. Of course you do not have any obligation. But the lady, who gave the answer below, did it, and could give a very good an detailed answer. Stackoverflow is a really interesting or strang side. Anyway +1 for the good answer — A M, Mar 25 '23 at 11:43
@Peter The problem with that answer is that it doesn't actually solve the problem that the poster is asking about, which is about some build errors. How would the OP learn about the errors he or she gets, and how to solve them by reading that answer? How would the OP learn anything about the basics of C++ and programming by just copy-pasting the code in that answer? And it really seems the OP is using that site to learn the basics, which aren't the purpose of such sites. — Some programmer dude, Mar 25 '23 at 12:06

score 1 · Accepted Answer · answered Mar 25 '23 at 11:34

Just looking at the code, the answer would be simple. The function should return an std::string and you return and int. You could be tempted now to solve the issue by using the to_string function and convert the int to a std:string.

But, this will not work.

The solution should and must work with strings.

Constraints:
    1 <= k <= nums.length <= 104
    1 <= nums[i].length <= 100
    nums[i] consists of only digits.
    nums[i] will not have any leading zeros.

It is obvious that you cannot store 100 digits long numbers in an int. So, you must also use sorting with strings.

But this will make life difficult, because you then need to employ so called natural sorting.

Example: Looking a 2,3 and 200, then, if you compare string, 3 will be greater than 200. And that is what the guys want from you. Natural sorting.

There are many solutions possible. Here is one of them:

#include <iostream>
#include <string>
#include <cctype>
#include <algorithm>
#include <vector>
using namespace std::string_literals;

// FUNCTOR for Natural sort function. Limited to signed char strings
struct NaturalSort {

    bool operator ()(const std::string& s1, const std::string& s2) {

        // We want to iterate over both strings
        const char* i1 = s1.data(); // Get a pointer to the beginning of string 1
        const char* i2 = s2.data(); // Get a pointer to the beginning of string 2

        // Result of comparison. 0 means equal, positive means s1>s2, negative means s1<s2
        int result = 0;
        // As long as both characters/numbers are equal and there are still characters in the string
        do {
            // If we found a digit at the same position in both strings
            if (std::isdigit(*i1) and std::isdigit(*i2)) {

                std::size_t pos1{}, pos2{}; // This will later indicate how many digits we read
                // Convert the strings to numbers and compare them
                result = std::stoi(i1, &pos1) - std::stoi(i2, &pos2);
                // Set pointers to the position after the number
                i1 += pos1; i2 += pos2;
            }
            else {
                // Normal character
                result = (*i1 - *i2);
                ++i1; ++i2;
            }
        } while ((result == 0) and (*i1 != 0 or *i2 != 0));
        // Let's limit the output to -1, 0 ,1
        return result < 0;
    }
};


class Solution{
public:
    std::string kthLargestNumber(std::vector<std::string>& nums, int k) {
        std::sort(nums.begin(), nums.end(), NaturalSort());
        return nums[nums.size()-k];
    }
};

// Driver / test code
int main() {
    std::vector<std::string> test{ "2"s,"3"s,"20"s,"30"s,"200"s,"300"s };
    Solution solution{};
    for (int k = 1; k <= test.size(); ++k) 
        std::cout << "With k=" << k << " the result would be: " << solution.kthLargestNumber(test, k) << '\n';
}

Why stoi() function is not working in the following code?

1 Answers1