Java数据结构和算法-二分查找

二分查找：

  二分查找又称折半查找，它是一种效率较高的查找方法。

  二分查找要求：线性表是有序表，即表中结点按关键字有序，并且要用向量作为表的存储结构。不妨设有序表是递增有序的。

二分查找递归和非递归Java实现：

package com.algorithm.search;

import com.algorithm.sort.BasicSort;

public class BinarySearch {

    public static void main(String[] args) {
        int[] a={3,4,5,1,98,45,34,27,49,6,78};
        int low=0;
        int high=a.length-1;
        int elem=45;
        BasicSort b=new BasicSort();
        b.basicSort(a);
        for(int num:a){
            System.out.print(" "+num);
        }
//        binarySearch(a,elem,low,high);
        directbinarySearch(a,elem,low,high);
    }

    /**
     *递归二分查找
     */
    public static int binarySearch(int[] a,int elem,int low,int high) {
        if (low <=high) {
            int mid = (low + high) / 2;
            if (a[mid] == elem) {
                System.out.println("递归二分查找找到该元素对应的下表：" + mid);
                return mid;
            }
            if (a[mid] > elem) {
                return binarySearch(a, elem, low, mid - 1);
            }
            if (a[mid] < elem) {
                return binarySearch(a, elem, mid + 1, high);
            }
        }
        return -1;
    }
    /**
     * 非递归二分查找
     */
    public static int directbinarySearch(int[] a,int elem,int low,int high) {
        while(low<=high){
            int mid = (low + high) / 2;
            if(a[mid] == elem){
                System.out.println("非递归二分查找找到该元素对应的下表：" + mid);
                return mid;
            }
            if (a[mid] > elem) {
                high=mid-1;
            }
            if(a[mid] < elem){
                low=mid+1;
            }

        }
        return -1;
    }
}
输出： 1 3 4 5 6 27 34 45 49 78 98非递归二分查找找到该元素对应的下表：7