lintcode-medium-Delete Digits

public class Solution {
    /**
     *@param A: A positive integer which has N digits, A is a string.
     *@param k: Remove k digits.
     *@return: A string
     */
    public String DeleteDigits(String A, int k) {
        // write your code here
        
        if(A == null || A.length() == 0)
            return A;
        
        String str = A;
        
        for(int i = 0; i < k; i++){
            int index = 0;
            for(; index < str.length() - 1; index++){
                if(str.charAt(index) > str.charAt(index + 1))
                    break;
            }
            
            str = str.substring(0, index) + str.substring(index + 1);
        }
        
        while(str.charAt(0) == ‘0‘)
            str = str.substring(1);
        
        return str;
    }
}