PermutationInString.java

package string;

/**
 * Created by gouthamvidyapradhan on 18/09/2017.
 * Given two strings s1 and s2, write a function to return true if s2 contains the permutation of s1. In other
 * words, one of the first string's permutations is the substring of the second string.

 Example 1:
 Input:s1 = "ab" s2 = "eidbaooo"
 Output:True
 Explanation: s2 contains one permutation of s1 ("ba").

 Example 2:
 Input:s1= "ab" s2 = "eidboaoo"
 Output: False
 Note:
 The input strings only contain lower case letters.
 The length of both given strings is in range [1, 10,000].

 */
public class PermutationInString {
    private int[] S1 = new int[256];
    private int[] S2 = new int[256];

    /**
     * Main method
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception{
        System.out.println(new PermutationInString().checkInclusion("ab", "eidboaoo"));
    }

    public boolean checkInclusion(String s1, String s2) {
        if(s2.length() < s1.length()) return false;
        for(int i = 0, l = s1.length(); i < l; i ++){
            S1[s1.charAt(i)] ++;
            S2[s2.charAt(i)] ++;
        }
        if(isEqual()) return true;
        for(int i = 1, j = s1.length(), l = s2.length(); j < l; i++, j++){
            S2[s2.charAt(i - 1)] --;
            S2[s2.charAt(j)] ++;
            if(isEqual()) return true;
        }
        return false;
    }

    private boolean isEqual(){
        boolean equal = true;
        for(int i = 0; i < 256; i ++){
            if(S1[i] != S2[i]){
                equal = false;
                break;
            }
        }
        return equal;
    }

}