java - How do I get the numerical value/position of a character in the alphabet (1-26) in constant time (O(1)) without using any built in method or function? -

how numerical value/position of character in alphabet (1-26) in constant time (o(1)) without using built in method or function , without caring case of character?

if compiler supports binary literals can use

int value = 0b00011111 & character; 

if not, can use 31 instead of 0b00011111 since equivalent.

int value = 31 & character; 

or if want use hex

int value = 0x1f & character; 

or in octal

int value = 037 & character; 

you can use way represent value 31.

this works because in ascii, undercase values prefixed 011, , uppercase 010 , binary equivalent of 1-26. using bitmask of 00011111 , and operand, covert 3 significant bits zeros. leaves 00001 11010, 1 26.