今天开始刷题啦，坚持住哟！

使用二分法的前提是数组有序且无重复元素。

704.二分查找

第一遍代码如下：

class Solution {public int search(int[] nums, int target) {int left=0;int right=nums.length-1;while(left<=right){int mid = (right-left)/2;if (nums[mid]>target){right=mid-1;}else if(nums[mid]<target){left=mid+1;}else if(nums[mid]==target){return mid;}}return -1;}
}

存在错误：

1. 没有考虑target小于nums[0]和大于nums[length-1]

2. mid计算错误，且没有防止溢出，以下是两种正确写法

int mid = left + ((right - left) / 2);

int mid = left + ((right - left) >> 1);

第二遍代码如下：

class Solution {public int search(int[] nums, int target) {if (target < nums[0] || target > nums[nums.length - 1]) {return -1;}int left=0;int right=nums.length-1;while(left<=right){int mid = left+((right-left)/2);if (nums[mid]>target){right=mid-1;}else if(nums[mid]<target){left=mid+1;}else if(nums[mid]==target){return mid;}}return -1;}
}

 测试通过！

35.搜索插入位置

第一遍代码：

class Solution {public int searchInsert(int[] nums, int target) {int left = 0;int right = nums.length-1;while(left<=right){int mid = left + ((right - left)/2);if (nums[mid]==target){return mid;}else if(nums[mid]>target){right = mid -1;}else{left=mid+1;}}return right+1;}
}

测试通过！