Occurrence of each element
Problem Statement – ?Todo
//Using Map
HashMap<Character,Integer> occuranceCount=new HashMap<>();
for(int i=0;i<arr.length();i++){
occuranceCount.put(arr[i],occuranceCount.getOrDefault(arr[i],0)+1));
}
//without using additional DS
Convert character to lowerToUpperCase and vice-versa
//1- using magic number 32
char a = 'a';
a -= 32;
System.out.println("a is " + a); //a is A
//2 binary operations
//2.1 lower to Upper use binary &
The binary AND operation: (l & 0x5f)
i.e System.out.println((char)('l' & 0x5f));
//2.1 Upper to lower use binary XOR ^
i.e System.out.println((char)(('L' ^ 0x20));
//3 using inbuilt function of Character class
char fUpper = Character.toUpperCase('f');
char lUpper = Character.toUpperCase('l')';
//How it works:
Binary, hex and decimal table:
------------------------------------------
| Binary | Hexadecimal | Decimal |
-----------------------------------------
| 1011111 | 0x5f | 95 |
------------------------------------------
| 100000 | 0x20 | 32 |
//Hints -ASCII codes
A-65, Z-90
a-97,z-122
Matrix -Properties
- Properties of Matrix [ N x N ]
- Major Diagonal Identification – rowNumber==colNUmber
- i.e rowNumber and col number are same
- Minor Diagonal Identification – rowNumber+colNUmber=total size of Matrix
- sum of rowNumber and col number is equal to total size of matrix
Bug Free Input in Java
Skip UNNECESSARY input:
After Input user presses <Enter> key which is not accepted by current input so, to avoid it being taken as input of next statement,Skip the special cases like newline(\n), line-separator (\u2028), paragraph separator (\u2029) etc.
int n = scanner.nextInt();
scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
Probable ArrayIndexOutOfBound -Graceful handling
Problem :
- 2 staring arrays S1 -length 2 and S2 lenght – 3, so accessing the elements without AIOB-
- Use case- LC -Version comparison
for(int i=0;i<maxLen;i++){
//here maxLen is bigger len i.e 3
int a1=i>s1.length?0:s1[i];
int a2=i>s2.length?0:s2[i];
//in above we checked length and returned compensatory rult -0 or actual
}
Techglot 