1.3 Given two strings, write a method to decide if one is a permutation of the other.

gistfile1.java

/* Time complexity O(nlogn), Space complexity O(1)  */

class Solution1{
  
  boolean isPerm(String s1, String s2){
    if(s1==null||s2==null) return false;
    if(s1.length()!=s2.length()) return false;
    char[] arr1 = s1.toCharArray();
    char[] arr2 = s2.toCharArray();
    Arrays.sort(arr1);
    Arrays.sort(arr2);
    for(int i=0; i<=s1.length()-1; i++){
      if(arr1[i]!=arr2[i])
        return false;
    }
    return true;
  } //
} // end sol1


/*Time complexity: O(n), Space complexity: O(n)*/
class Solution2{
  
  boolean isPerm(String s1, String s2){
    if(s1==null||s2==null) return false;
    if(s1.length()!=s2.length()) return false;
    
    int[] temp = new int[256];
    for(int i=0; i<=s1.length()-1; i++){
      char c = s1.charAt(i);
      temp[c]++;
    }
    for(int j=0; j<=s2.length()-1; j++){
      char c2 = s2.charAt(j);
      temp[c2]--;
      if(temp[c2]<0){
        return false;
      }
    }
    return true;
  }
} // end sol2