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Author: wuduhren

problems/group-anagrams.py

@@ -14,3 +14,23 @@ def groupAnagrams(self, strs):
             for c in s: hashkey[ord(c)-97] +=1
             anagrams[''.join(hashkey)].append(s)
         return anagrams.values()
+
+"""
+Time: O(NK), N is the number of strings, K is the number of characters in the string.
+Space: O(NK).
+"""
+class Solution(object):
+    def groupAnagrams(self, strs):
+        anagrams = collections.defaultdict(list)
+        
+        for s in strs:
+            anagrams[self.getKey(s)].append(s)
+        
+        return anagrams.values()
+    
+    def getKey(self, s):
+        key = ''
+        counts = collections.Counter(s)
+        for c in 'abcdefghijklmnopqrstuvwxyz':
+            key += counts[c]*c
+        return key

problems/ugly-number-ii.py

@@ -0,0 +1,31 @@
+"""
+`ans` contains sorted ugly numbers.
+For each ugly number we can x2 or x3 or x5 to produce another ugly number.
+
+i2 points at the number that has been x2 yet.
+i3 points at the number that has been x3 yet.
+i5 points at the number that has been x5 yet.
+
+Each time we append one minimum ugly number and move the pointer.
+
+Time: O(N)
+Space: O(N)
+"""
+class Solution(object):
+    def nthUglyNumber(self, k):
+        i2 = i3 = i5 = 0
+        
+        ans = [1]
+        while len(ans)<k:
+            n2 = ans[i2]*2
+            n3 = ans[i3]*3
+            n5 = ans[i5]*5
+            
+            n = min(n2, n3, n5)
+            ans.append(n)
+            
+            if n2==n: i2 += 1
+            if n3==n: i3 += 1
+            if n5==n: i5 += 1
+                
+        return ans[-1]

problems/ugly-number.py

@@ -0,0 +1,9 @@
+class Solution(object):
+    def isUgly(self, n):
+        if n<1: return False
+        
+        while n%2==0: n /= 2
+        while n%3==0: n /= 3
+        while n%5==0: n /= 5
+            
+        return n==1