56.Merge-Intervals.md

56. Merge Intervals

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题目地址

https://leetcode.com/problems/merge-intervals/

题目描述

Given a collection of intervals, merge all overlapping intervals.

Example 1:
Input: [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].
Example 2:

Input: [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considered overlapping.
NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.

代码

Approach #2 Sorting

class Solution {
	public int[][] merge(int[][] intervals) {
		if (intervals.length <= 1)  return intervals;

		// Sort by ascending starting point
		Arrays.sort(intervals, (i1, i2) -> i1[0] - i2[0]);

		List<int[]> result = new ArrayList<>();
		int[] prevInterval = intervals[0];
		result.add(prevInterval);
		for (int[] interval : intervals) {
			if (interval[0] <= prevInterval[1]) {
        // Overlapping intervals, move the end if needed
				prevInterval[1] = Math.max(prevInterval[1], interval[1]);
      } else {                             
        // Disjoint intervals, add the new interval to the list
				prevInterval = interval;
				result.add(prevInterval);
			}
		}

		return result.toArray(new int[result.size()][]);
	}
}