Create c++ tricks

c++ tricks

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+1) Checking if the number is even or odd without using the % operator:
+Although this trick is not much better than using % operator but is sometimes efficient (with large numbers). Use & operator:
+
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+if (num & 1) 
+   cout << "ODD"; 
+else
+   cout << "EVEN"; 
+Example:
+num = 5
+Binary: “101 & 1” will be 001, so true
+num = 4
+Binary: “100 & 1” will be 000, so false.
+#######################################################################################################
+2) Fast Multiplication or Division by 2
+Multiplying by 2 means shifting all the bits to left and dividing by 2 means shifting to the right.
+
+Example : 2 (Binary 10): shifting left 4 (Binary 100) and right 1 (Binary 1)
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+n = n << 1;   // Multiply n with 2 
+n = n >> 1;   // Divide n by 2 
+########################################################################################################
+3) Swapping of 2 numbers using XOR:
+This method is fast and doesn’t require the use of 3rd variable.
+
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+// A quick way to swap a and b 
+a ^= b; 
+b ^= a; 
+a ^= b;
+#######################################################################################################
+4) Calculating the most significant digit: To calculate the most significant digit of any number log can be directly used to calculate it.
+
+Suppose the number is N then 
+Let double K = log10(N);
+now K = K - floor(K);
+int X = pow(10, K);
+X will be the most significant digit.
+##########################################################################################################
+5) Calculating the number of digits directly: To calculate number of digits in a number, instead of looping you can efficiently use log :
+
+Number of digits in N =floor(log10(N)) + 1;
+#########################################################################################################
+6) Efficient trick to know if a number is a power of 2 sing the normal technique of division the complexity comes out to be O(logN), but it can be solved using O(v) where v are the number of digits of number in binary form.
+
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+/* Function to check if x is power of 2*/
+bool isPowerOfTwo (int x) 
+{ 
+  /* First x in the below expression is  
+    for the case when x is 0 */
+  return x && (!(x&(x-1))); 
+  ############################################################################################################
+  7) The Iota Algorithm The algorithm iota() creates a range of sequentially increasing values, as if by assigning an initial value to *first, then incrementing that value using prefix ++. In the following listing, iota() assigns the consecutive values {10, 11, 12, 13, 14} to the array arr, and {‘a’, ‘b’, ‘c’} to the char array c[].
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+int a[5] = {0}; 
+char c[3] = {0}; 
+
+// changes a to {10, 11, 12, 13, 14} 
+iota(a, a+5, 10);  
+iota(c, c+3, 'a'); // {'a', 'b', 'c'}
+##############################################################################################################
+8) Initialization in Binary form: In C++ 11 assignments can also be made in binary form.
+
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+// C++ code to demonstrate working of  
+// "binary" numbers 
+#include<iostream> 
+using namespace std; 
+int main() 
+{ 
+    auto number = 0b011; 
+    cout << number; 
+    return 0; 
+} #########################################################################################################
+9) Use of “and” Though not a very productive one, this tip helps you to just use conditional operator and instead of typing &.
+
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+// C++ code to demonstrate working of "and" 
+#include<iostream> 
+using namespace std; 
+int main() 
+{ 
+    int a = 10; 
+    if (a < 20 and a > 5) 
+      cout << "Yes"; 
+    return 0; 
+}#################################################################################################################333
+10) Use of emplace_back() (Discussed here, here and here)
+Instead of push_back() in STL emplace_back can be used because it is much faster and instead of allocating memory somewhere else and then appending it directly allocates memory in the container.
+
+11) Inbuilt GCD function: C++ has inbuilt GCD function and there is no need to explicitly code it. Syntax: __gcd(x, y);
+
+12) Using Inline functions: We can create inline functions and use them without having to code them up during the contest. Examples: (a) function for sieve, (b) function for palindrome.
+
+13) Maximum size of the array: We must be knowing that the maximum size of array declared inside the main function is of the order of 10^6 but if you declare array globally then you can declare its size upto 10^7.
+