Use binary search to locate an item in an array. - Java Data Structure

Java examples for Data Structure:Binary Search

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Description

Use binary search to locate an item in an array.

Demo Code

import java.security.SecureRandom;
import java.util.Arrays;

public class Main {
  public static int binarySearch(int[] data, int key) {
    int low = 0; // low end of the search area
    int high = data.length - 1; // high end of the search area
    int middle = (low + high + 1) / 2; // middle element
    int location = -1; // return value; -1 if not found

    do {//from   w  ww  .jav  a2s  . c o m
      System.out.print(remainingElements(data, low, high));

      for (int i = 0; i < middle; i++)
        System.out.print("   ");
      System.out.println(" * "); // indicate current middle

      // if the element is found at the middle
      if (key == data[middle])
        location = middle; // location is the current middle
      else if (key < data[middle]) // middle element is too high
        high = middle - 1; // eliminate the higher half
      else
        // middle element is too low
        low = middle + 1; // eliminate the lower half

      middle = (low + high + 1) / 2; // recalculate the middle
    } while ((low <= high) && (location == -1));

    return location;
  }

  private static String remainingElements(int[] data, int low, int high) {
    StringBuilder temporary = new StringBuilder();

    // append spaces for alignment
    for (int i = 0; i < low; i++)
      temporary.append("   ");

    // append elements left in array
    for (int i = low; i <= high; i++)
      temporary.append(data[i] + " ");

    return String.format("%s%n", temporary);
  }

  public static void main(String[] args) {
    SecureRandom generator = new SecureRandom();

    int[] data = new int[15]; // create array

    for (int i = 0; i < data.length; i++)
      // populate array
      data[i] = 10 + generator.nextInt(90);

    Arrays.sort(data); // binarySearch requires sorted array
    System.out.printf("%s%n%n", Arrays.toString(data)); // display array

    int searchInt = 123;

    // perform search
    int location = binarySearch(data, searchInt);

    if (location == -1) // not found
      System.out.printf("%d was not found%n%n", searchInt);
    else
      // found
      System.out.printf("%d was found in position %d%n%n", searchInt, location);
  }
}

Result


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