binary search

budd-common/src/main/java/io/github/ehlxr/algorithm/search/BinarySearch.java

@@ -0,0 +1,95 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright © 2022 xrv <xrg@live.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package io.github.ehlxr.algorithm.search;
+
+/**
+ * @author ehlxr
+ * @since 2022-01-01 17:06.
+ */
+public class BinarySearch {
+    public static void main(String[] args) {
+        int[] a = new int[]{1, 3, 5, 6, 7, 8, 9};
+        System.out.println(search(a, a.length, 3));
+        System.out.println(searchRec(a, a.length, 3));
+    }
+
+    /**
+     * 非递归二分查找
+     *
+     * @param a 要查找的数组
+     * @param n 数组的长度
+     * @param v 要查找的值
+     * @return 要查找值在数组中的索引
+     */
+    public static int search(int[] a, int n, int v) {
+        int low = 0;
+        int high = n - 1;
+        while (low <= high) {
+            int mid = low + (high - low) >> 1;
+            if (a[mid] == v) {
+                return mid;
+            }
+
+            if (a[mid] < v) {
+                low = mid + 1;
+            } else {
+                high = mid - 1;
+            }
+        }
+        return -1;
+    }
+
+    /**
+     * 递归二分查找
+     *
+     * @param a 要查找的数组
+     * @param n 数组的长度
+     * @param v 要查找的值
+     * @return 要查找值在数组中的索引
+     */
+    public static int searchRec(int[] a, int n, int v) {
+        return searchRec(a, 0, n - 1, v);
+    }
+
+    /**
+     * 递归二分查找
+     */
+    public static int searchRec(int[] a, int low, int high, int v) {
+        if (low > high) {
+            return -1;
+        }
+
+        int mid = low + (high - low) >> 1;
+        if (a[mid] == v) {
+            return mid;
+        }
+
+        if (a[mid] < v) {
+            return searchRec(a, mid + 1, high, v);
+        } else {
+            return searchRec(a, low, mid - 1, v);
+        }
+    }
+}