readme update, group-anagrams.py, open-the-lock.py

Author: Chris Wu

README.md

@@ -22,6 +22,8 @@ CS DoJo on "How I Got a Job at Google as a Software Engineer". There are also lo
 1. <https://www.quora.com/How-should-I-prepare-for-my-Google-interview-if-I-have-1-month-left-and-I%E2%80%99m-applying-for-a-software-engineer-role/answer/Anthony-D-Mays?ch=10&share=5c488000&srid=W0jqp>
 2. <https://www.quora.com/How-can-I-get-a-job-at-Facebook-or-Google-in-6-months-I-need-a-concise-work-plan-to-build-a-good-enough-skill-set-Should-I-join-some-other-start-up-or-build-my-own-projects-start-up-Should-I-just-focus-on-practicing-data-structures-and-algorithms/answer/Jimmy-Saade>
 3. <https://www.quora.com/What-should-I-know-from-the-CLRS-3rd-edition-book-if-my-aim-is-to-get-into-Google/answer/Jimmy-Saade>
+4. Leetcode Topics  
+<https://docs.google.com/spreadsheets/d/1SbpY-04Cz8EWw3A_LBUmDEXKUMO31DBjfeMoA0dlfIA/edit#gid=126913158>
 
 ## Resume
 <https://drive.google.com/file/d/10b9NZDhPbUOW_C7108IKe9ev6Ed2UG7F/view>

problems/group-anagrams.py

@@ -4,4 +4,13 @@ def groupAnagrams(self, strs):
         anagrams = collections.defaultdict(list)
         for s in strs:
             anagrams[''.join(sorted(s))].append(s)
-        return anagrams.values()
+        return anagrams.values()
+
+class Solution(object):
+    def groupAnagrams(self, strs):
+        anagrams = collections.defaultdict(list)
+        for s in strs:
+            hashkey = [0]*26
+            for c in s: hashkey[ord(c)-97] +=1
+            anagrams[''.join(hashkey)].append(s)
+        return anagrams.values()

problems/open-the-lock.py

@@ -0,0 +1,70 @@
+"""
+In priority queue, we not only take `steps` in to consideration but also `distance`
+And the rest is just like dijkstra.
+"""
+import heapq
+class Solution(object):
+    def openLock(self, deadends, target):
+        def getNeighbor(node):
+            opt = []
+            for i in xrange(len(node)):
+                if node[i]==0:
+                    opt.append(tuple(node[:i]+(1,)+node[i+1:]))
+                    opt.append(tuple(node[:i]+(9,)+node[i+1:]))
+                elif node[i]==9:
+                    opt.append(tuple(node[:i]+(0,)+node[i+1:]))
+                    opt.append(tuple(node[:i]+(8,)+node[i+1:]))
+                else:
+                    opt.append(tuple(node[:i]+(node[i]+1,)+node[i+1:]))
+                    opt.append(tuple(node[:i]+(node[i]-1,)+node[i+1:]))
+            return opt
+
+        def getDistance(node):
+            distance = 0
+            for i in xrange(len(node)):
+                d = abs(int(node[i])-int(target[i]))
+                d2 = abs(10-d)
+                distance+=min(d, d2)
+            return distance
+
+        def tupify(node):
+            return tuple(map(int, node))
+
+        target = tupify(target)
+        visited = set([tupify(node) for node in deadends])
+        pq = [(0, 0, tupify('0000'))]
+
+        while pq:
+            _, steps, node = heapq.heappop(pq)
+            if node==target: return steps
+            if node in visited: continue
+            visited.add(node)
+            for nei in getNeighbor(node):
+                heapq.heappush(pq, (steps+1+getDistance(nei), steps+1, nei))
+        return -1
+
+class Solution:
+    def openLock(self, deadends, target):
+        def getNeighbor(node):
+            opt = []
+            for i in xrange(len(node)):
+                add_one = delta[node[i]][0]
+                minus_one = delta[node[i]][1]
+                opt.append(node[:i]+add_one+node[i+1:])
+                opt.append(node[:i]+minus_one+node[i + 1:])
+            return opt
+
+        delta = {str(i): [str((i+1)%10), str((i-1)%10)] for i in xrange(10)}
+        visited = set(deadends)
+        q = collections.deque([('0000', 0)])
+        steps = 0
+
+        while q:
+            node, steps = q.popleft()
+            if node==target: return steps
+            if node in visited: continue
+            visited.add(node)
+            for nei in getNeighbor(node):
+                q.append((nei, steps+1))
+
+        return -1