二分查找(折半查找)

 [要求] 1. 必须采用顺序存储结构； 2.必须按关键字大小有序排列。

/**     * 折半查找     * @param arr     * @param searchValue     * @return     */    public static int binarySearch(int[] arr, int searchValue) {        if(arr == null) {            return -1;        }                int low = 0;        int high = arr.length -1;                while(low <= high) {            int midIndex = (low + high)/2;                        if(arr[midIndex] == searchValue) {                return midIndex;            }else if(arr[midIndex] > searchValue) {                high = midIndex - 1;            }else{                low = midIndex + 1;            }                    }                return -1;            }            /**     * 二分查找，特殊实现     * @param arr     * @param searchValue     * @param first     * @param last     * @return     */    public static int binarySearch(int[] arr, int searchValue, int first,int last) {        if(arr == null) {            return -1;        }                if(searchValue < arr[first] || searchValue > arr[last]) {            return -1;        }                int midIndex = (first+last)/2;                if(searchValue < arr[midIndex]) {            return binarySearch(arr, searchValue, first, midIndex-1);        }else if(searchValue > arr[midIndex]){            return binarySearch(arr, searchValue, midIndex + 1, last);        }else {            return midIndex;        }            }