Mon, 01 Jan 0001 00:00:00 +0000

binary search #

implement #

import org.junit.Assert;
import org.junit.Test;

public class BinarySearch {

 @Test
 public void testBinarySearch(){
 int[] arr = new int[]{4,8,10, 16,18,20,50,100};

 Assert.assertEquals("", binarySearch(arr, 0, arr.length - 1, 4), 0);
 Assert.assertEquals("", binarySearch(arr, 0, arr.length - 1, 16), 3);
 Assert.assertEquals("", binarySearch(arr, 0, arr.length - 1, 100), 7);
 Assert.assertEquals("", binarySearch(arr, 0, arr.length - 1, 12302), -1);
 }

 private static int binarySearch(int[] arr, int left, int right, int key) {
 if(left > right) { return -1;}

 int mid = (left + right) / 2;
 int midKey = arr[mid];

 if(key > midKey){ return binarySearch(arr, mid + 1, right, key); }

 // right = mid - 1 才对，不然会发生 StackOverflowError, 比如： Assert.assertEquals("", binarySearch(arr, 0, arr.length - 1, 2), -1);
 // if(key < midKey){ return binarySearch(arr, left, mid, key); }
 if(key < midKey){ return binarySearch(arr, left, mid - 1, key); }
 return mid;
 }
}

Reference #

https://www.bilibili.com/video/BV1E4411H73v?p=82&vd_source=550a4dc4b2a914c0681a14307bbe8cbe

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binary search #

implement #

Reference #