Pointers for competitive programming C++
This shot will discuss certain
Tip 1: Use \n instead of endl
When you submit the coding solution on an online coding platform, we get to see the
One solution is to avoid the use of endl to print the next line character in your solution. This is because the endl operator prints the new line character, but it also flushes the output stream, which leads to a higher execution time. For a lower execution time, use \n.
Tip 2: Use bits/stdc++.h
When working with bits/stdc++.h, the header file for all the libraries in C++.
Tip 3: Use typedef
Generally, in competitive coding contests, you do not have time to declare long data type declarations like vector<int, int> or vector<pair<int, int>, bool>.
Instead, use typedef to declare these type names at the start of your program. Then, they can easily be used whenever you require them in the rest of the code.
Let’s look at the code below to better understand this.
Code
#include <bits/stdc++.h>using namespace std;typedef long long ll;typedef vector<int> vi;typedef vector<pair<int, bool>> vpib;int main() {ll a = 123456789;cout << a << "\n";vi vec = {1,2,3,4,5};vpib vpair = {{1,true}, {2, false}};return 0;}
Explanation
-
In line 1, we used
bits/stdc++.hto import all the header files instead of importing each of them one by one. -
From lines 4 to 6, we used
typedefto declare the type names. -
In the
main()function, we used thetype names Declared in the previous step
Tip 4: Use macros
Macros replace certain statements in the code before the compilation. They help reduce the effort of writing the same thing again and again in the code.
For example, imagine you have a vector and you use the push_back() method to insert an element into the vector. Here, you can create a PB macro that will be replaced every time as push_back. Macros can also have parameters.
Let’s look at the code below to understand this better.
Code
#include <bits/stdc++.h>using namespace std;#define PB push_back#define MP make_pair#define FIN(a , b) for(int i = a; i < b; i++)int main() {vector<int> vec;vec.PB(10);vec.PB(20);FIN(0, vec.size())cout << vec[i] << " ";return 0;}
Explanation
- In lines 4 to 6, we created three macros. In line 6, we created a macro with parameters.
- In lines 10 and 11, we used the
PBmacro instead of usingpush_back. - In line 13, we used a macro to run a loop.
Macros can thus be useful to reduce repeated code and write the code faster.
Tip 5: Use cin in a loop
In many problems, we are given a stream of inputs where we do not know how many inputs there are. We can use cin in a loop, where the loop accepts the input until your input becomes NULL. Let’s look at the code below to understand this better.
Code
Enter a number below.
#include <iostream>using namespace std;int main() {// your code goes hereint n;while(cin >> n){cout << n << " ";}}
Enter the input below
Explanation:
- In line 7, we set the condition of the
whileloop to run until there are no more inputs present.
This will allow you to enter any number of inputs.
These tips will hopefully help you to write code in better and faster ways.
Check out my course Competitive Programming - Crack Your Coding Interview, C++ to help you prepare for your upcoming coding interviews.
