问题描述:
Given a sorted integer array without duplicates, return the summary of its ranges.
Example 1:
Input: [0,1,2,4,5,7]
Output: ["0->2","4->5","7"]
Explanation: 0,1,2 form a continuous range; 4,5 form a continuous range.
Example 2:
Input: [0,2,3,4,6,8,9]
Output: ["0","2->4","6","8->9"]
Explanation: 2,3,4 form a continuous range; 8,9 form a continuous range.
源码:
我自己的下做法,很冗余,就是用Left和right存储左右边界。如果left = right-1说明只有一个元素。
时间100%,空间34%
class Solution {
public:
vector<string> summaryRanges(vector<int>& nums) {
int n = nums.size();
vector<string> result;
if(n==0) return result;
if(n==1){
result.push_back(to_string(nums[0])); return result;
}
int left = 0, right = 1;
for (right=1; right<n; right++){
// cout<<right<<endl;
while (right<n && nums[right] == nums[right-1] + 1) right++;
if(left != right-1){
result.push_back(to_string(nums[left]) + "->" + to_string(nums[right-1]));
left = right;
}
else {
result.push_back(to_string(nums[left]));
left = right;
}
if (right == n-1) result.push_back(to_string(nums[n-1]));
}
return result;
}
};
翻了一下Discuss区大佬的做法,思路都差不多,有个很简洁的方法。时间同样100%:
class Solution {
public:
vector<string> summaryRanges(vector<int>& nums)
{
vector<string> result;
int n = nums.size();
for (auto left(0), right(0); right<n; right++){
if(right==n-1 || nums[right+1]!=nums[right]+1){
result.emplace_back(left==right? to_string(nums[right]): to_string(nums[left])+"->"+to_string(nums[right]));
left = right+1;
}
}
return result;
}
};
其中emplace_back和push_back的差别如下:
push_bach():
首先需要调用构造函数构造一个临时对象,然后调用拷贝构造函数将这个临时对象放入容器中,然后释放临时变量。
emplace_back():
这个元素原地构造,不需要触发拷贝构造和转移构造。