[LeetCode] 052: Merge Intervals

[Problem]

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].

[Solution]

/**
 * Definition for an interval.
 * struct Interval {
 *     int start;
 *     int end;
 *     Interval() : start(0), end(0) {}
 *     Interval(int s, int e) : start(s), end(e) {}
 * };
 */
 
/**
 * Definition for cmp
 */
bool cmp(const Interval &a, const Interval &b){
	return a.start < b.start;
}

/**
 * Definition for Solution
 */
class Solution {
public:
	// merge interval into intervals
	void merge(vector<Interval> &intervals, Interval interval){
		// intervals is empty
		if(intervals.size() == 0){
			intervals.push_back(interval);
		}
		else{
			int i = intervals.size()-1;

			// not interacted with the last interval
			if(interval.start > intervals[i].end){
				intervals.push_back(interval);
			}
			// interacted with the last interval, update the end of the last interval
			else{
				intervals[i].end = max(intervals[i].end, interval.end);
			}
		}
	}
	// merge intervals
	vector<Interval> merge(vector<Interval> &intervals) {
		// Start typing your C/C++ solution below
		// DO NOT write int main() function
		vector<Interval> res;

		// sort by start
		sort(intervals.begin(), intervals.end(), cmp);

		// merge
		for(int i = 0; i < intervals.size(); ++i){
			merge(res, intervals[i]);
		}
		return res;
	}
};

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