Best time to Buy and sell stock

help
, , ,
1

I am doing this question from leetcode where I am getting an error .can somebody help me to find it?I have tried dry running it 2 times sitll i am not able to debug it.

Problem link:

class Solution {
public:
    int maxProfit(vector<int>& prices) {
    long long int n=prices.size();
        
        vector<int> profit(n,0);
       vector<int> suffix(n,0);
        suffix[n-1]=prices[n-1];
        profit[n-1]=0;
        
        for(long long int i=n-2;i>=0;i++)
        {
            suffix[i]=max(suffix[i+1],prices[i+1]);
            profit[i]=suffix[i]-prices[i];
        }
        
        int ans =0;
        for(long long int i=0;i<n;i++)
            ans=max(ans,profit[i]);
        
        return ans;
        
    }
};
2

i-- in first for loop

3

can you give me any on tips how can i avoid making such mistakes? :sweat_smile: :sweat_smile:
i tried debugging it for long time by checking each line still i do these mistakes(and this is not the first time :slightly_smiling_face: :slightly_smiling_face:)

4

Just running the sample input with proper debug flags would have spotted this immediately:

#include <iostream>
#include <vector>

using namespace std;

class Solution {
public:
    int maxProfit(vector<int>& prices) {
    long long int n=prices.size();
        
        vector<int> profit(n,0);
       vector<int> suffix(n,0);
        suffix[n-1]=prices[n-1];
        profit[n-1]=0;
        
        for(long long int i=n-2;i>=0;i++)
        {
            suffix[i]=max(suffix[i+1],prices[i+1]);
            profit[i]=suffix[i]-prices[i];
        }
        
        int ans =0;
        for(long long int i=0;i<n;i++)
            ans=max(ans,profit[i]);
        
        return ans;
        
    }
};

int main()
{
    vector<int> sampleInputPrices = {7,1,5,3,6,4};
    cout << Solution().maxProfit(sampleInputPrices) << endl;
}

[simon@simon-laptop][19:05:01]
[~/devel/hackerrank/otherpeoples]>./compile-latest-cpp.sh 
Compiling abhinav_700-blah.cpp
+ g++ -std=c++17 abhinav_700-blah.cpp -O3 -g3 -Wall -Wextra -Wconversion -DONLINE_JUDGE -D_GLIBCXX_DEBUG -fsanitize=undefined -ftrapv -fno-sanitize-recover
+ set +x
Successful
[simon@simon-laptop][19:05:04]
[~/devel/hackerrank/otherpeoples]>./a.out 
/usr/include/c++/7/debug/vector:417:
Error: attempt to subscript container with out-of-bounds index 6, but 
container only holds 6 elements.

Objects involved in the operation:
    sequence "this" @ 0x0x7ffe48851f90 {
      type = std::__debug::vector<int, std::allocator<int> >;
    }
Aborted (core dumped)
5

My compiler doesn’t throw such verbose error message. What debugger you are using?

6

All the information you need is there :slight_smile:

7

Can you tell me which flag is responsible?

8

In this particular case: -D_GLIBCXX_DEBUG

9

Ok thanks!

1 Like
10

so i guess i sould start learning debugging