1、条件
-
查找的数量只能是一个,不能是多个;
-
用于查找的内容逻辑上是有序无重复的;
2、分类
3、思想
- 判断左右值和target大小规定左右索引范围;
- 循环条件一定要和区间分类一致,两种区间循环条件也不一致;
- 左闭右闭循环不加等号会出现找不到target;左闭右开循环加等号,当值在数组里没有时,跳不出循环并输出-1
4、代码
- 左闭右闭
int search(vector<int>& nums; int target)
{
int left = 0;
int right = nums.size() - 1;
while (left <= right)
{
int middle = (left + right)/2;
if (nums[middle] < target)
{
left = middle + 1;
}
else if(nums[middle] > target)
{
right = middle - 1;
}
else
{
return middle;
}
}
return -1;
}
- 左闭右开
int search(vector<int>& nums; int target)
{
int left = 0;
int right = nums.size() - 1;
while (left < right)
{
int middle = (left + right)/2;
if (nums[middle] < target)
{
left = middle + 1;
}
else if(nums[middle] > target)
{
right = middle;
}
else
{
return middle;
}
}
return -1;
}