SuffixArray.java

package com.interview.suffixprefix;

import java.util.Arrays;
import java.util.Comparator;

/**
 http://www.geeksforgeeks.org/suffix-array-set-1-introduction/
 */
public class SuffixArray {

    public static class SuffixSort implements Comparator<Integer>{
        
        private char str[] = null;
        
        public SuffixSort(char str[]){
            this.str = str;
        }
        
        @Override
        public int compare(Integer i1, Integer i2) {
            while(i1 < str.length && i2 < str.length && str[i1] == str[i2]){
                i1++;
                i2++;
            }
            if(i2 == str.length && i1 == str.length){
                return 0;
            }
            else if(i1 == str.length){
                return -1;
            }else if(i2 == str.length){
                return 1;
            }else return str[i1] < str[i2] ? -1 : 1;
            
        }
    }
    
    public Integer[] createSuffixArray(char str[]){
    
        SuffixSort sort = new SuffixSort(str);
        Integer suffix[] = new Integer[str.length];
        for(int i=0; i < suffix.length; i++){
            suffix[i] = i;
        }
        Arrays.sort(suffix,sort);
        return suffix;  
    }
    
    private int stringCompare(char str[],char subString[],int pos){
        int i=0;
        while(pos < str.length && i < subString.length && str[pos] == subString[i]){
            pos++;
            i++;
        }
        if(i == subString.length){
            return 0;
        }
        if(pos == str.length){
            return -1;
        }
        return str[pos] < subString[i] ? -1 : 1;  
    }
    
    public int subStringSearch(char str[],char subString[], Integer suffix[]){
        int low =0;
        int high = suffix.length-1;
        while(low <= high){
            int mid = (low + high)/2;
            int result = stringCompare(str, subString, suffix[mid]);
            if(result == 0){
                return suffix[mid];
            }
            if(result > 0){
                high = mid-1;
            }else{
                low = mid+1;
            }
        }
        return -1;
    }
    
    public static void main(String args[]){
        SuffixArray suffix = new SuffixArray();
        String str = "missisippi";
        Integer result[] = suffix.createSuffixArray(str.toCharArray());
        System.out.print(suffix.subStringSearch(str.toCharArray(), "sippi".toCharArray(), result));
    }
}