基础算法5——二分查找

import java.util.*;

public class BinarySearch {

    public static void main(String[] args) {
        ArrayList<Integer> a = new ArrayList<Integer>();
        addIntegerInSequence(a, 1, 10);
        print(a);
        int pos = binarySearch(a, 10);
        if (pos != -1) {
            System.out.print("Element found: " + pos);
        } else {
            System.out.print("Element not found");
        }
    }

    /**
     * 二分查找法
     * 
     * @param a
     * @param value
     *            待查找元素
     * @return
     */
    public static int binarySearch(ArrayList<Integer> a, int value) {
        int size = a.size();
        int low = 0, high = size - 1;
        int mid;
        while (low <= high) {
            mid = (low + high) / 2;
            if (a.get(mid) < value) {
                low = low + 1;
            } else if (a.get(mid) > value) {
                high = high - 1;
            } else {
                return mid;
            }
        }
        return -1;
    }

    /**
     * 填充顺序元素到数组
     * 
     * @param a
     * @param begin
     *            开始元素
     * @param size
     *            大小
     */
    public static void addIntegerInSequence(ArrayList<Integer> a, int begin,
            int size) {
        for (int i = begin; i < begin + size; i++) {
            a.add(i);
        }
    }

    /**
     * 打印数组
     * 
     * @param a
     */
    public static void print(ArrayList<Integer> a) {
        Iterator<Integer> i = a.iterator();
        while (i.hasNext()) {
            System.out.print(i.next() + " ");
        }
        System.out.println("");
    }

}