gistfile1.java

// Write a program that converts a human readable column header into a column index. 
// A column header is an arbitrary length string of the characters A through Z, e.g: "A", "B", "AB", "BA" or "AAK".
// A represents the first column and its index is 1, B is the second with an index of 2, AA is the 27th column, etc.
 
// The program should read the column header from standard in and print the result to standard out as a string of digits. 
// Given an input string of "A" the program should output only "1".
//
// Note that you can compile and test your code in the browser multiple times before submitting.
 
import java.io.BufferedReader; 
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
 
public class Solution {
    public static void main(String[] args) throws Exception {
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            String input; 
            while ((input = br.readLine()) != null) {
                System.out.println(convert(input));
            }
        } catch(IOException io) {
            io.printStackTrace();
        }
          
//          System.out.println(convert("A"));  // #=> 1
//          System.out.println(convert("C"));  // #=> 3
//          System.out.println(convert("AA")); // #=> 27
//          System.out.println(convert("KL")); // #=> 298
    }
    
    public static int convert(String columnHeader) {
        final char[] alphabets = new char[] {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
            'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
            'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'
        };
 
        HashMap<Character, Integer> index = new HashMap<Character, Integer>();
        for (int i = 1; i < alphabets.length; i++) {
            index.put(alphabets[i - 1], i);
        }
        
        // AA = 26 * 1 + 1 
        // AAA = 26 * 26 * 1 + 26 * 1 + 1
        // KL = 26 * 11 + 12
        int acc = 0;
        int pos = columnHeader.length() - 1;
        for (char each : columnHeader.toCharArray()) {
            int mult = (int) Math.pow(26, pos);
            acc = acc + index.get(each) * mult;
            pos--;
        }
        return acc;
    }
}