题目链接:35. 搜索插入位置
代码1:
class Solution {
public:
int searchInsert(vector<int>& nums, int target) {
int left = 0, right = nums.size()-1;
while(left<=right){
int mid = left + (right-left)/2;
if(target<nums[mid]){
right = right - 1;
}else if(target > nums[mid]){
left = left + 1;
}else{
return mid;
}
}
return right + 1;
}
};
代码2:
class Solution {
public:
int searchInsert(vector<int>& nums, int target) {
int left = 0, right = nums.size();
while(left<right){
int mid = left + (right-left)/2;
if(target<nums[mid]){
right = right - 1;
}else if(target > nums[mid]){
left = left + 1;
}else{
return mid;
}
}
return right;
}
};
mid=(left+right)/2
存在问题。
原因:left可能不断增大,如果到极限状态,也就是left达到了right-1的地步的时候刚好数组的长度又很大,那么就可能导致left + right的溢出出现负数;
mid=left+(right-left)/2或mid=left+((right-left)>>2)
(right+left)相加的结果可能会导致整型溢出的情况,(right-left)使用减法不会超出最大的整型范畴;
>>是右移运算符,右移一位相当于除2,右移n位相当于除以2的n次方;mid=(left+right)>>1等价于mid=(left+right)/2;
left+(right-left)/2通分可知是等同于 (left + right) / 2;