small fixes

Author: lilianweng

LCA.py

@@ -17,9 +17,12 @@ def lca(root, a, b):
     if root.value == a or root.value == b: return root
     left = lca(root.left, a, b)
     right = lca(root.right, a, b)
-    if left and right: # if p and q are on both sides
+    if left and right: 
+        # a & b are on both sides
         return root
-    else: # either a/b is on one side OR a/b is not in L&R subtrees
+    else: 
+        # EITHER a/b is on one side 
+        # OR a/b is not in L&R subtrees
         return left if left else right
 
 

scramble_str.py

@@ -98,25 +98,28 @@ def scramble_str1(s1, s2):
 # a | tten <---> tten | a
 # ti | on <---> it | no
 # o | n <---> n | o
-
 # t | i <---> i | t
+def elem(s):
+    return ''.join(sorted(s))
+
+def same_elems(s1, s2):
+    return elem(s1) == elem(s2)
+
 def matching(s1, s2):
     #print s1, s2
     if s1 == s2: return True
     if len(s1) != len(s2): return False
     for i in range(1,len(s1)):
         x1, y1 = s1[:i], s1[i:]
-        
         x2, y2 = s2[:i], s2[i:]
-        if (''.join(sorted(x1)) == ''.join(sorted(x2))) and \
-           (''.join(sorted(y1)) == ''.join(sorted(y2))) and \
+        x3, y3 = s2[-i:], s2[:-i]
+        
+        if same_elems(x1,x2) and same_elems(y1,y2) and \
            matching(x1, x2) and matching(y1, y2):
             return True
 
-        x3, y3 = s2[-i:], s2[:-i]
-        if (''.join(sorted(x1)) == ''.join(sorted(x3))) and \
-           (''.join(sorted(y1)) == ''.join(sorted(y3))) and \
-           matching(x1, x3) and matching(y1, y3):
+        if same_elems(x1,x3) and same_elems(y1,y3) and \
+           matching(x1,x3) and matching(y1,y3):
             return True
 
     return False

valid_sudoku.py

@@ -31,6 +31,32 @@ def check_conflict(M, x, y, val):
     return False
 
 
+# whether the sudoku is valid
+def is_valid_sudoku(M):
+    N = 9
+    assert len(M) == N and len(M[0]) == N
+    # row; no repetition between 0~9.
+    for i in range(N):
+        if not valid_array(M[i]):
+            return False
+    # col
+    for j in range(N):
+        if not valid_array([M[i][j] for i in range(N)]):
+            return False
+    
+    # 3x3 cells
+    for x in range(0,9,3):
+        for y in range(0,9,3):
+            A = [M[i][j] for i in range(x,x+3) for j in range(y,y+3)]
+            if not valid_array(A):
+                return False
+    return True
+
+
+def valid_array(A):
+    if len(set(A)) == len(A) and min(A) >= 1 and max(A) <= 9: return True
+    return False
+
 
 if __name__ == '__main__':
     M = [[5,3,0,0,7,0,0,0,0],