Cp branch

Competitive_Programming/C++/Time Limit Exceeded Error/TLE.md

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+# TLE - Time Limit Exceeded Error
+
+In CP, we face this error when the code submitted takes more time to execute than accepted. There are few assumptions made by C++ programmer which is not true.
+
+1. Header File
+
+ ``` c++
+  #include<bits/stdc++.h>
+  using namespace std;
+
+```
+
+normally you find this on the top of the code of c++ coders. <bits/stdc++.h> is a very large header file .
+It has all the headers that one could need for CP in it but also have many other headers that take more compilation time.
+This would not effect Time execution online but it should be avoided if we want a very efficient solution.
+
+2. The best method to avoid TLE is to work more on bits than on operators or prebuild functions
+
+like:
+
+**for swapping two numbers**
+```c++
+
+//for swapping two numbers
+a^=b
+b^=a
+a^=b
+
+```
+ **for determing if a number is even or odd**
+```c++
+
+// for determining if a number is even or odd
+if(number & 1)
+  cout<<"number is odd";
+else
+  cout<<"number is even";
+
+```
+
+**for multiplication a number with 2^n**
+```c++
+
+//for multiplication of a number with 2^n
+number<<n;
+
+```
+**for division a number with 2^n**
+```c++
+
+//for division a number with 2^n
+number>>n;
+
+```
+
+**check if a number is a power of 2**
+
+```c++
+
+bool isPowerOf2( int n )
+{
+  return ( n && (!(n & ( n-1 ) ) );
+  }
+
+```
+
+3. Input Output 
+
+In C++, scanf and printf work faster than cin and cout this happens due to synchronization.
+So if we don't want to use scanf and printf in C++. we should turn off the synchronization.
+
+```c++
+
+ios_base :: sync_with_stdio(false);
+
+```
+4. Time Space Trade
+ If we want less time , we can increase the space it might help in reducing the space similarly,
+ if we wish to use less space than time might increase.
+
+ These are some observations and tricks to save yourself from TLE error.