1+ import java .util .Arrays ;
12import java .util .HashMap ;
23import java .util .Random ;
34
@@ -131,6 +132,30 @@ public static long fact(int N) {
131132 return N * fact (N - 1 );
132133 }
133134
135+ /**
136+ * static method that calls rank to binary search for "key"
137+ * */
138+ public static int binarySearch (int key , int [] array ) {
139+ Arrays .sort (array ); // we need the array to be sorted
140+ return rank (key , array , 0 , array .length - 1 );
141+ }
142+ 143+ 144+ /**
145+ * static recursive method that implements binary search
146+ * */
147+ public static int rank (int key , int [] array , int minIndex , int maxIndex ) {
148+ if (minIndex > maxIndex ) return -1 ;
149+ int midIndex = minIndex + (maxIndex - minIndex ) / 2 ;
150+ 151+ if (array [midIndex ] == key ) return midIndex ;
152+ 153+ if (array [midIndex ] < key )
154+ return rank (key , array , midIndex + 1 , maxIndex );
155+ else
156+ return rank (key , array , minIndex , maxIndex - 1 );
157+ }
158+ 134159
135160 public static void main (String [] args ) {
136161 Random generator = new Random ();
@@ -142,6 +167,19 @@ public static void main(String[] args) {
142167 boolean [][] testTwoDmBooleanArray = new boolean [3 ][2 ];
143168 int [][] testIntMatrix = new int [3 ][2 ];
144169
170+ int [] testIntArray = new int [10 ];
171+ 172+ testIntArray [0 ] = 5 ;
173+ testIntArray [1 ] = 7 ;
174+ testIntArray [2 ] = 6 ;
175+ testIntArray [3 ] = 9 ;
176+ testIntArray [4 ] = 3 ;
177+ testIntArray [5 ] = 8 ;
178+ testIntArray [6 ] = 2 ;
179+ testIntArray [7 ] = 4 ;
180+ testIntArray [8 ] = 1 ;
181+ testIntArray [9 ] = 10 ;
182+ 145183 testTwoDmBooleanArray [0 ][0 ] = true ;
146184 testTwoDmBooleanArray [0 ][1 ] = false ;
147185 testTwoDmBooleanArray [1 ][0 ] = false ;
@@ -189,5 +227,9 @@ public static void main(String[] args) {
189227
190228 System .out .printf ("31!: %d\n " , fact (31 )); // N > 31 causes overflow
191229 System .out .println ();
230+ 231+ System .out .println ("- Binary Search: key = 5" );
232+ System .out .println (binarySearch (5 , testIntArray ));
233+ System .out .println ();
192234 }
193235}
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