力扣刷题 704.二分查找--day1
解法
一、暴力解法
//暴力解法
int search(vector<int>& nums, int target) {
for(int i = 0; i<nums.size(); i++){
if(nums[i] == target)
return i;
}
return -1;
}
二、二分查找
//二分查找
int search(vector<int> &nums, int target){
int left = 0;
int right = nums.size() - 1;
while(left <= right){
// int mid = (left + right) / 2;
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 -1;
}
错误点:
- 二分查找中的截止条件判断错误
where(left <= right) 中忘记相等的情况
小技巧:
- 计算 middle 时, 为了防止整数相加溢出
可以将下列式子修改:
int mid = (left + right) / 2;
改为:
int mid = left + (right - left)/2;