Find the smallest window in a string containing all characters of another string (With smallest window)

Given two strings string1 and string2, find the smallest substring in string1 containing all characters of string2 efficiently.
For Example:

Steps:

• Generate all substrings which starts with any one character from the pattern string
• Iterate all substrings which we generated and compare each character from the pattern string with the substring and check for all characters present or not
• If all characters present in substring then trim extra characters and choose the smallest window string

Java code:

public class StringInSmallestWindow {

 public static void main(String[] args) {

  String str = "niharika";
  String findStr = "ir";
  String result = null;

  if (str.length() < findStr.length()) {
   System.out.println("Pattern string is greater than source string");
   return;
  }

  int j = 0;
  String[] arr = new String[str.length()];
  // Get all substring which starts with any one character from the
  // pattern string
  for (int i = 0; i < str.length(); i++) {
   if (findStr.contains(str.charAt(i) + "") && str.substring(i).length() >= findStr.length()) {
    arr[j++] = str.substring(i);
   }
  }

  // Iterate all substrings which we generated
  for (int pnt = 0; pnt < j; pnt++) {

   String string = arr[pnt];
   char[] tmp = findStr.toCharArray();

   int cnt = tmp.length;
   int lastIndex = 0;

   // Compare each character from the pattern string with the substring
   // and check for all characters present or not
   for (int i = 0; i < tmp.length; i++) {

    if (string.contains(tmp[i] + "")) {
     if (lastIndex < string.indexOf(tmp[i])) {
      lastIndex = string.indexOf(tmp[i]);
     }
     string = string.substring(0, string.indexOf(tmp[i])) + '\0'
       + string.substring(string.indexOf(tmp[i]) + 1);
     tmp[i] = '\0';
     cnt--;
    }
   }

   // If all characters present in substring then trim extra characters
   // and choose the smallest window string
   if (cnt <= 0) {
    arr[pnt] = arr[pnt].substring(0, lastIndex + 1);
    result = arr[pnt].length() < result.length() ? arr[pnt] : result;
   }

  }
  System.out.println("\nInput String           : " + str);
  System.out.println("\n2nd String to find     : " + findStr);
  System.out.println("\nSmallest window string : " + result);
 }
}

OUTPUT:

Input String           : niharika

2nd String to find     : ir

Smallest window string : ri