no message

Author: Chris Wu

problems/meeting-rooms-ii.py

@@ -29,11 +29,13 @@ def minMeetingRooms(self, intervals):
 
         return result
 
-        # Definition for an interval.
-        # class Interval(object):
-        #     def __init__(self, s=0, e=0):
-        #         self.start = s
-        #         self.end = e
+
+
+# Definition for an interval.
+# class Interval(object):
+#     def __init__(self, s=0, e=0):
+#         self.start = s
+#         self.end = e
 
 class Solution(object):
     def minMeetingRooms(self, intervals):

problems/meeting-rooms.py

@@ -0,0 +1,16 @@
+"""
+Time: O(NLogN)
+Space: O(1)
+
+Sort the interval (mainly by start time), see if the end overlaps with the start of next.
+"""
+class Solution(object):
+    def canAttendMeetings(self, intervals):
+        intervals.sort()
+        
+        for i in xrange(len(intervals)-1):
+            end = intervals[i][1]
+            nextStart = intervals[i+1][0]
+            if end>nextStart: return False
+        
+        return True

problems/top-k-frequent-elements.py

@@ -59,4 +59,33 @@ def topKFrequent(self, nums, k):
         return opt
 
 
+"""
+Time: O(N+KLogN).
+Building numToCounts takes O(N).
+Building heap takes O(N) (Yeah, I know. Some People thinks `heapify` takes O(NLogN) but it actually takes O(N). But that is another story...).
+HeapPop takes O(LogN).
+
+Space: O(N)
+
+1. Form `[(-count1, num1), (-count2, num2)]`, in this case `h`.
+Use "-count" its because heapq in python is min heap, so using negative value will make it pop out the most freq count.
 
+2. Turn h into heap. (heapify)
+
+3. HeapPop h for k times.
+"""
+class Solution(object):
+    def topKFrequent(self, nums, k):
+        ans = []
+        
+        numToCounts = collections.Counter(nums)
+        h = [(-numToCounts[num], num) for num in numToCounts]
+        
+        heapq.heapify(h)
+        
+        while k>0:
+            _, num = heapq.heappop(h)
+            ans.append(num)
+            k -= 1
+        
+        return ans