线性表查找(顺序查找，二分查找)

1、顺序查找(无序)
2、折半查找(必须是有序数组)

实现代码(java)

public class lineSearch {
    //测试代码
    public static void main(String[] args) {
        //顺序查找
        int[] arr1 = {34,76,23,98,87,35,8,32,74,44};
        int key = 8;
        System.out.println(key+"出现的索引为："+search(arr1,8));//6

        //二分法查找（有序数组）
        int[] arr2 = {1,2,3,4,5,6,7,8,9,10};

        //非递归方式
        System.out.println(key+"出现的索引为："+myBinarySearch(arr2,8));//7

        //递归方式
        System.out.println(key+"出现的索引为："+myBinarySearch2(arr2,8));//7
    }

    /**
     * 时间复杂度：T(n) = O(logn)
     * 空间复杂度:S(n) = O(logn)
     * 递归二分法查找
     * @param arr
     * @param key
     * @return
     */
    private static int myBinarySearch2(int[] arr, int key) {
        int low = 0;
        int high = arr.length;
        return binarySearch(arr,key,low,high);
    }
    //递归方法
    private static int binarySearch(int[] arr, int key,int low,int high) {
        int mid = (low+high)/2;
        if(key == arr[mid]){
            return mid;
        }else if(key < arr[mid]){
            return binarySearch(arr,key,low,mid -1);
        }else if(key > arr[mid]){
            return binarySearch(arr,key,mid+1,high);
        }

        return -1;
    }

    /**
     * 时间复杂度: T(n) = O(logn)
     * 空间复杂度：S(n) = O(1)
     * 非递归二分法查找
     * @param arr
     * @param key
     * @return
     */
    private static int myBinarySearch(int[] arr, int key) {
        int low = 0;
        int high = arr.length;
        int mid = 0;

        while(low<=high){
            mid = (high + low)/2;
            if(key == arr[mid]){
                return mid;
            }else if (key<arr[mid]){
                high = mid - 1;
            }else{
                low = mid + 1;
            }
        }
        return -1;
    }

    /**
     * 时间复杂度：T(n) = O(n)
     * 空间复杂度：S(n) = O(1)
     * 顺序查找
     * @param arr
     * @param key
     * @return
     */
    private static int search(int[] arr, int key) {
        if(arr == null || arr.length ==0){
            return -1;
        }
        for(int i = 0;i<arr.length;i++){
            if(arr[i] == key){
                return i;
            }
        }
        return -1;
    }
}