Merge Intervals

最新推荐文章于 2025-09-05 23:16:08 发布

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#leetcode

本文介绍了一种有效的合并区间算法，该算法通过两种方法实现：使用插入区间方法和使用比较器方法。通过对输入区间的排序和合并操作，可以高效地解决区间重叠问题，并返回合并后的区间列表。

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:

Using insert interval:

/**
 * Definition for an interval.
 * public class Interval {
 *     int start;
 *     int end;
 *     Interval() { start = 0; end = 0; }
 *     Interval(int s, int e) { start = s; end = e; }
 * }
 */
public class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        List<Interval> merged = new ArrayList<Interval>();
        for (Interval i: intervals) {
            List<Interval> list = new ArrayList<Interval>();
            for (Interval j: merged) {
                if (i.start > j.end)
                    list.add(j);
                else if (i.end < j.start) {
                    list.add(i);
                    i = j;
                }
                else
                    i = new Interval(Math.min(i.start, j.start), Math.max(i.end, j.end));
            }
            list.add(i);
            merged = new ArrayList<Interval>(list);
        }
        return merged;
    }
}

Using Comparator:

/**
 * Definition for an interval.
 * public class Interval {
 *     int start;
 *     int end;
 *     Interval() { start = 0; end = 0; }
 *     Interval(int s, int e) { start = s; end = e; }
 * }
 */
public class Solution {
    public List<Interval> merge(List<Interval> intervals) {
        if (intervals == null || intervals.size() <= 1)
            return intervals;
        List<Interval> merged = new ArrayList<Interval>();
        Collections.sort(intervals, new IntervalComparator());
        Interval pre = intervals.get(0);
        for (int i = 1; i < intervals.size(); i++) {
            Interval cur = intervals.get(i);
            if (cur.start > pre.end) {
                merged.add(pre);
                pre = cur;
            }
            else {
                cur = new Interval(pre.start, Math.max(pre.end, cur.end));
                pre = cur;
            }
        }
        merged.add(pre);
        return merged;
    }
    
    class IntervalComparator implements Comparator<Interval> {
        public int compare(Interval i1, Interval i2) {
            return i1.start - i2.start;
        }
    }
}