二分搜索

src/main/java/com/ximo/datastructuresinaction/algorithmsfourthedition/chapter01/BinarySearch.java

@@ -0,0 +1,52 @@
+package com.ximo.datastructuresinaction.algorithmsfourthedition.chapter01;
+
+import java.util.Arrays;
+
+/**
+ * @author xikl
+ * @date 2020/4/25
+ */
+public class BinarySearch {
+
+    public static int binarySearchByRecursive(int[] array, int key) {
+        if (array == null || array.length == 0) {
+            return -1;
+        }
+
+        // 排序
+        Arrays.sort(array);
+        return binarySearchByRecursive(array, key, 0, array.length);
+    }
+
+    /**
+     * 递归实现 二分搜索
+     *
+     * @param array
+     * @param key
+     * @param low
+     * @param high
+     * @return
+     */
+    public static int binarySearchByRecursive(int[] array, int key, int low, int high) {
+        if (low > high) {
+            return -1;
+        }
+
+        // 优化 为了看懂 high + ((low - high) >> 1);
+        int mid = high + (low - high) / 2;
+
+        // 卫语句
+        if (key < array[mid]) {
+            return binarySearchByRecursive(array, key, low, mid - 1);
+        }
+
+        if (key > array[mid]) {
+            return binarySearchByRecursive(array, key, mid + 1, high);
+        }
+
+        // 那就是等于
+        return mid;
+    }
+
+
+}

src/main/java/com/ximo/datastructuresinaction/algorithmsfourthedition/Chapter01.java → src/main/java/com/ximo/datastructuresinaction/algorithmsfourthedition/chapter01/IsPrime.java

@@ -1,10 +1,10 @@
-package com.ximo.datastructuresinaction.algorithmsfourthedition;
+package com.ximo.datastructuresinaction.algorithmsfourthedition.chapter01;
 
 /**
  * @author xikl
  * @date 2020/4/25
  */
-public class Chapter01 {
+public class IsPrime {
 
     public static boolean isPrime(int n) {
         // 大于1的数字才是
@@ -37,5 +37,4 @@ public static void main(String[] args) {
         System.out.println(isPrime(13));
     }
 
-
 }