LeetCode 56. Merge Intervals
Solution1:我的答案
这道题思路不能,有个坑爹的地方在于输入的区间向量未必是有序的,所以利用优先队列priority_queue来排序
/**
* Definition for an interval.
* struct Interval {
* int start;
* int end;
* Interval() : start(0), end(0) {}
* Interval(int s, int e) : start(s), end(e) {}
* };
*/
struct cmp {//学习定义priority_queue的比较函数
bool operator () (Interval &a, Interval &b) {
return a.start > b.start;
}
};
class Solution { // O(n)
public:
vector<Interval> merge(vector<Interval>& intervals) {
if (!intervals.size()) return {};
priority_queue<Interval, vector<Interval>, cmp> q(intervals.begin(), intervals.end());
vector<Interval> new_intervals;
while (!q.empty()) { //注意优先队列不能用迭代器
new_intervals.push_back(q.top());
q.pop();
}
vector<Interval> res;
res.push_back(new_intervals[0]);
for (int i = 1; i < new_intervals.size(); i++) {
if (res.back().end < new_intervals[i].start) {
res.push_back(new_intervals[i]);
} else {
res.back().start = min(res.back().start, new_intervals[i].start);
res.back().end = max(res.back().end, new_intervals[i].end);
}
}
return res;
}
};
priority_queue用法
官网链接:http://www.cplusplus.com/reference/queue/priority_queue/?kw=priority_queue
自定义比较函数连接:https://blog.csdn.net/Allenlzcoder/article/details/80885979
注意:priority_queue没有迭代器
常用的函数有
empty(): Test whether container is empty (public member function )
size(): Return size (public member function )
top(): Access top element (public member function )
push(): Insert element (public member function )
emplace(): Construct and insert element (public member function )
pop(): Remove top element (public member function )
swap(): Swap contents (public member function )
Solution2:参考答案
链接:http://www.cnblogs.com/grandyang/p/4370601.html
/**
* Definition for an interval.
* struct Interval {
* int start;
* int end;
* Interval() : start(0), end(0) {}
* Interval(int s, int e) : start(s), end(e) {}
* };
*/
bool cmp (Interval &a, Interval &b) {
return a.start < b.start;
}
class Solution {
public:
vector<Interval> merge(vector<Interval>& intervals) {
if (intervals.empty()) return {};
//关于sort()函数自定义比较函数还是得学习一个!
sort(intervals.begin(), intervals.end(), cmp);
vector<Interval> res{intervals[0]};
for (int i = 1; i < intervals.size(); ++i) {
if (res.back().end < intervals[i].start) {
res.push_back(intervals[i]);
} else {
res.back().end = max(res.back().end, intervals[i].end);
}
}
return res;
}
};
关于sort()的自定义比较函数,参考网址:https://blog.csdn.net/pmt123456/article/details/61191348
写在类内时,要加上static,lexicographical_compare 最后要求的是一个普通函数指针,而不是成员函数指针,所以要加static。
都忘了,是时候好好复习一下了~~~