二分查找demo

Author: mj

app/src/main/java/com/mj/android_note/data_structure/DataStructureDemo.java

@@ -4,6 +4,8 @@
 
 import androidx.annotation.NonNull;
 
+import com.mj.android_note.data_structure.algorithm.binary.BinarySearchUtils;
+
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Iterator;
@@ -74,6 +76,10 @@ public static void main(String[] args) {
         // 3.LinkedHashMap是如何保证按照访问顺序，将数据存在链表的尾部的。
         // 4.HashMap中的entrySet是何拿值的
 
+        // 二分查找测试
+        int[] sortArray = {1, 2, 3, 4, 5, 6, 8, 10, 100, 111, 126};
+        int i = BinarySearchUtils.binarySearch(sortArray, 100);
+        printLog("binary search target index : " + i);
     }
 
     private static void printMap(Map<String, Integer> map) {

app/src/main/java/com/mj/android_note/data_structure/algorithm/binary/BinarySearchUtils.java

@@ -0,0 +1,37 @@
+package com.mj.android_note.data_structure.algorithm.binary;
+
+/**
+ * Author      : MJ
+ * Date        : 2020-03-17--13:53
+ * Email       : [email protected]
+ * Description : 二分查找法
+ */
+public class BinarySearchUtils {
+
+    /**
+     * 二分查找
+     *
+     * @param array  给定一个数组
+     * @param target 目标值要找的目标值
+     * @return 目标值在数组中的索引
+     */
+    public static int binarySearch(int[] array, int target) {
+        int startIndex = 0;
+        int endIndex = array.length - 1;
+        int searchCount = 0;
+        while (startIndex <= endIndex) {
+            int midIndex = (startIndex + endIndex) / 2;
+            int val = array[midIndex];
+            searchCount++;
+            if (target > val) {
+                startIndex = midIndex + 1;
+            } else if (target < val) {
+                endIndex = midIndex - 1;
+            } else {
+                System.out.println("search count : " + searchCount);
+                return midIndex;
+            }
+        }
+        return ~startIndex;
+    }
+}