finish 56

Author: BaffinLee

56. Merge Intervals.js

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+/**
+ * 56. Merge Intervals
+ * 
+ * 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 considerred overlapping.
+ */
+
+/**
+ * Definition for an interval.
+ * function Interval(start, end) {
+ *     this.start = start;
+ *     this.end = end;
+ * }
+ */
+/**
+ * @param {Interval[]} intervals
+ * @return {Interval[]}
+ */
+var merge = function(intervals) {
+	var len = intervals.length;
+	var res = [];
+	var a = null;
+	var b = null;
+
+	intervals.sort((c, d) => (c.start - d.start));
+
+	for (var i = 0; i < len; i++) {
+			a = res[res.length - 1];
+			b = intervals[i];
+			if (overlap(a, b)) {
+					a.start = Math.min(a.start, b.start);
+					a.end = Math.max(a.end, b.end);
+			} else {
+					res.push(new Interval(b.start, b.end));
+			}
+	}
+
+	return res;
+};
+
+var overlap = function (a, b) {
+	if (!a || !b) return false;
+	if (b.start <= a.end && a.end <= b.end) return true;
+	if (a.start <= b.end && b.end <= a.end) return true;
+	return false;
+};
+
+// 先排序，后操作
+// 也可以边操作边排序