1.1 二分查找(线性表-数组)——【leetcode】

1.1 二分查找(线性表-数组)——【leetcode】

package com.arrays.java;

import org.junit.Test;

public class one {
	
	//方法一：左闭右闭区间
	 public int search(int[] nums, int target) {
		 //首先做个判断，target落在nums数组的区间内
		 if(target < nums[0] || target > nums[nums.length - 1]) {
			 return -1;
		 }
		 
		 int left = 0, right = nums.length - 1;
		 while(left <= right) {
			 int mid = left + ((right - left) >> 1);
			 if(nums[mid] == target) {
				 return mid;
			 }else if(nums[mid] < target) {
				 left = mid + 1;
			 }else if(nums[mid] > target) {
				 right = mid - 1;
			 }
		 }		 
		 return -1;
	 }
	 
	 //方法二：左闭右开区间
	 public int search1(int[] nums, int target) {
		//首先做个判断，target落在nums数组的区间内
		 if(target < nums[0] || target > nums[nums.length - 1]) {
			 return -1;
		 }
		 
		 int left = 0, right = nums.length;//注意这里不是nums.length-1
		 
		 while(left < right) {
			 int mid = left + (right - left)/2;
			 if(nums[mid] == target) {
				 return mid;
			 }else if(nums[mid] < target) {
				 left = mid + 1;//左闭区间 左边就是+1
			 }else if(nums[mid] > target) {
				 right = mid;//右开区间 这边就不用-1
			 }
		 }
		 return -1;
	 }
	 
	 @Test
	 public void test() {
		 System.out.println((3-0)>>1);//1  相当于（3-0）/2
	 }
	

}