算法精粹(algorithm-essentials)

感谢soulmachine@github提供内容
## Merge Intervals


### 描述

Given a collection of intervals, merge all overlapping intervals.

For example,
Given `[1,3],[2,6],[8,10],[15,18]`,
return `[1,6],[8,10],[15,18]`


### 分析

复用一下Insert Intervals的解法即可,创建一个新的interval集合,然后每次从旧的里面取一个interval出来,然后插入到新的集合中。


### 代码

{% if book.java %}
```java
// Merge Interval
//复用一下Insert Intervals的解法即可
// 时间复杂度O(n1+n2+...),空间复杂度O(1)
public class Solution {
public List merge(List intervals) {
List result = new ArrayList<>();
for (int i = 0; i < intervals.size(); i++) {
insert(result, intervals.get(i));
}
return result;
}
private static List insert(List intervals,
Interval newInterval) {
for (int i = 0; i < intervals.size();) {
final Interval cur = intervals.get(i);
if (newInterval.end < cur.start) {
intervals.add(i, newInterval);
return intervals;
} else if (newInterval.start > cur.end) {
++i;
continue;
} else {
newInterval.start = Math.min(newInterval.start, cur.start);
newInterval.end = Math.max(newInterval.end, cur.end);
intervals.remove(i);
}
}
intervals.add(newInterval);
return intervals;
}
}
```
{% endif %}

{% if book.cpp %}
```cpp
// Merge Interval
//复用一下Insert Intervals的解法即可
// 时间复杂度O(n1+n2+...),空间复杂度O(1)
class Solution {
public:
vector merge(vector &intervals) {
vector result;
for (int i = 0; i < intervals.size(); i++) {
insert(result, intervals[i]);
}
return result;
}
private:
vector insert(vector &intervals, Interval newInterval) {
vector::iterator it = intervals.begin();
while (it != intervals.end()) {
if (newInterval.end < it->start) {
intervals.insert(it, newInterval);
return intervals;
} else if (newInterval.start > it->end) {
it++;
continue;
} else {
newInterval.start = min(newInterval.start, it->start);
newInterval.end = max(newInterval.end, it->end);
it = intervals.erase(it);
}
}
intervals.insert(intervals.end(), newInterval);
return intervals;
}
};
```
{% endif %}


### 相关题目

* [Insert Interval](insert-interval.md)