二分查找（面试必会知识点）

//递归
    public int recursionSearch(int[] arr, int key, int low, int high) {
        if(key < arr[low] || key > arr[high] || low > high) {
            return -1;
        }

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



   //迭代
    public int commonSearch(int[] arr, int key) {
        int low = 0;
        int high = arr.length - 1;
        int mid = 0;

        if(key < arr[low] || key > arr[high] || low > high) {
            return -1;
        }

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

        return -1;
    }