java之二分查找算法实现

/** * ">>" 右边移出去的部分扔掉不要，左边空出来的部分用原来的数字填充（这就是所谓的带符号右移） * ">>>" 右移 左边补0 */ /** * 二分查找（递归实现） * @param * @param array 有序数组 * @param from 起始下标 * @param to 终止下标 * @param key 需要查找的关键字 * @return * @throws Exception */ public static <E extends Comparable> int binarySearch(E[] array, int from, int to, E key) throws Exception { if (from < 0 || to < 0) { throw new IllegalArgumentException("params from & length must larger than 0 ."); } if (from <= to) { int middle = (from >>> 1) + (to >>> 1); // 右移即除2 E temp = array[middle]; if (temp.compareTo(key) > 0) { to = middle - 1; } else if (temp.compareTo(key) < 0) { from = middle + 1; } else { return middle; } } return binarySearch(array, from, to, key); } /** * 二分查找（非递归实现） * @param a 有序数组 * @param fromIndex 起始下标 * @param toIndex 终止下标 * @param key 需要查找的关键字 * @return */ private static int binarySearch0(int[] a, int fromIndex, int toIndex, int key) { int low = fromIndex; int high = toIndex - 1; while (low <= high) { int mid = (low + high) >>> 1; int midVal = a[mid]; if (midVal < key) low = mid + 1; else if (midVal > key) high = mid - 1; else return mid; // key found } return -(low + 1); // key not found. }