CS 101 Lecture 29 - Searching, Complexity of Algorithms

Class Examples:

1. An iterative method for finding 'num' in an unordered array (linear search):

     /*
      * Search for num in array.  Return the index of the number, or
      * -1 if it is not found.
      */
     int search(int[] array, int num) {
       for (int index = 0; index < array.length; index++) {
         if (array[index] == num) {
           return index;
         }
       }
       return -1;
     }
   

2. A recursive linear search method:

     /*
      * Search for num in array recursively. Return the index of the number, or
      * -1 if it is not found.
      */
     int recSearch(int[] array, int num, int start) {
       if (start >= array.length) {
         return -1;
       } else if (array[start] == num) {
         return start;
       } else {
         return recSearch(array, num, start + 1);
       }
     }
   

3. A recursive method for searching an ordered list (binary search):

     /*
      * Binary Search for num in array.  Pass in the low and high 
      * indices of the array for the range in which the number may
      * still occur.  Return the index of the number, or -1 if it
      * is not found.
      */
     int binarySearch(int[] array, int num, int low, int high) {
      if (low > high) {
         return -1;
       } else {
         int mid = (low + high) / 2;
         if (array[mid] == num) {
           // num is same as middle number
           return mid;
         } else if (num < array[mid]) {
           // num is smaller than middle number
           return binarySearch(array, num, low, mid - 1);
         } else {
           // num is larger than middle number
           return binarySearch(array, num, mid + 1, high);
         }
       }
     }