二分查找递归非递归

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前言：二分查找是针对于一组有序元素的查找算法，时间复杂度了O(logn)

直接上代码

public class BinarySearch {    public static void main(String[] args) {        int[] data = {1,4,6,7,9,12,16,78,98};        BinarySearch b = new BinarySearch();        int result = b.binarySearch(data, 1);        System.out.println(result);    }    //iterative    public int binarySearch(int[] data, int target) {//数组有序用二分查找,时间复杂度O(logn)        if (data == null || data.length == 0) return -1;//非法输入返回-1        int low = 0;        int high = data.length - 1;        int mid;        while (low <= high) {//有等于的情况即最后一次二分查找            //mid = (low + high) / 2;//在循环里面取中间值            mid = low + (high - low) >> 1;//用移位操作加快速度,同时考虑low + high溢出            if (target < data[mid]) {                high = mid - 1;            }            else if (target > data[mid]) {                low = mid + 1;            }            else {                return mid;            }        }        return -1;//找不到返回-1    }    //recursive    public int binarySearch2(int[] data, int low, int high, int target) {//递归法需要加low和high参数        if (data == null || data.length == 0) return -1;        if (low <= high) {            int mid = (low + high) / 2;            if (target < data[mid]) {                return binarySearch2(data, low, mid - 1, target);//要return            }            else if (target > data[mid]) {                return binarySearch2(data, mid + 1, high, target);            }            else {                return mid;            }        }        else {            return -1;        }    }}

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