12_Integer_to_Roman

13_Roman_to_Integer
54_Spiral_Matrix
137_Single_Number_II

Author: qiyuangong

README.md

@@ -12,14 +12,17 @@
 | 5 | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/5_Longest_Palindromic_Substring.py) | [Background knowledge](http://en.wikipedia.org/wiki/Longest_palindromic_substring)<br>1. DP if s[i]==s[j] and P[i+1, j-1] then P[i,j]<br>2. A palindrome can be expanded from its center<br>3. Manacher algorithm|
 | 7 | [Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/7_Reverse_Integer.py) | Overflow when the result is greater than 2147483647
 | 8 | [String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/8_String_to_Integer(atoi).py) | Overflow, Space, and negative number |
-| 9 | [Palindrome Number](https://leetcode.com/problems/palindrome-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/9_Palindrome_Number.py)| Get the len and check left and right with 10^len, 10|
+| 9 | [Palindrome Number](https://leetcode.com/problems/palindrome-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/9_Palindrome_Number.py)| Get the len and check left and right with 10^len, 10 |
+| 12 | [Integer to Roman](https://leetcode.com/problems/integer-to-roman/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/12_Integer_to_Roman.py) | [Background knowledge](http://www.rapidtables.com/convert/number/how-number-to-roman-numerals.htm) Just like 10-digit number, divide and minus |
+| 13 | [Roman to Integer](https://leetcode.com/problems/roman-to-integer/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/13_Roman_to_Integer.py) | Add all curr, if curr > prev, then need to subtract 2 * prev |
 | 15 | [3Sum](https://leetcode.com/problems/3sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/15_3Sum.py) | 1. Sort and O(n^2) search with three points <br>2. Multiple Two Sum (Problem 1) |
 | 16 | [3Sum Closest](https://leetcode.com/problems/3sum-closest/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/16_3Sum_Closest.py) | Sort and Multiple Two Sum check abs|
 | 18 | [4Sum](https://leetcode.com/problems/4sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/18_4Sum.py) | The same as 3Sum, but we can merge pairs with the same sum |
 | 21 | [Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/21_Merge_Two_Sorted_Lists.py) | Add a dummy head, then merge two sorted list in O(m+n) |
 | 23 | [Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/23_Merge_k_Sorted_Lists.py) | 1. Priority queue O(nk log k)<br>2. Binary merge O(nk log k)|  |
 | 24 | [Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/24_Swap_Nodes_in_Pairs.py) | Add a dummy and store the prev |
 | 28 | [Implement strStr()](https://leetcode.com/problems/implement-strstr/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/28_Implement_strStr().py) | 1. O(nm) comparison <br>2. KMP |
+| 54 | [Spiral Matrix](https://leetcode.com/problems/spiral-matrix/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/54_Spiral_Matrix.py) | O(nm) 1. Turn in the corner and loop<br>2. (0, 1) -> (1, 0) -> (0, -1) -> (-1, 0) |
 | 65 | [Valid Number](https://leetcode.com/problems/valid-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/65_Valid_Number.py) | 1. strip leading and tailing space, then check float using exception, check e using split <br>2. check is number split by . or e, note that number after e may be negative |
 | 66 | [Plus One](https://leetcode.com/problems/plus-one/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/66_Plus_One.py) | Check if current digit == 9. |
 | 72 | [Edit Distance](https://leetcode.com/problems/edit-distance/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/72_Edit_Distance.py) | [Background](https://en.wikipedia.org/wiki/Edit_distance)<br> 1. DP O(n^2) space<br>2. DP O(n) space |
@@ -31,7 +34,8 @@
 | 111 | [Minimum Depth of Binary Tree](https://leetcode.com/problems/minimum-depth-of-binary-tree/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/111_Minimum_Depth_of_Binary_Tree.py) | 1. Recursion, note that when size of left (ld) or right (rd) is 0, then min = 1 + ld + rd<br> 2. BFS check by level (right most), which is much faster than recursion |
 | 124 | [Binary Tree Maximum Path Sum](https://leetcode.com/problems/binary-tree-maximum-path-sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/124. Binary Tree Maximum Path Sum.py) | Recursion O(n) and O(n), max (left + node, right + node, left + node + right) |
 | 125 | [Valid Palindrome](https://leetcode.com/problems/valid-palindrome/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/125_Valid_Palindrome.py)| Exclude non-alphanumeric characters and compare O(n) |
-| 136 | [Single Number](https://leetcode.com/problems/single-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/136_Single_Number.py) | 1. Hash or set, O(n) and O(n)<br>2. xor O(n) and O(1) | 
+| 136 | [Single Number](https://leetcode.com/problems/single-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/136_Single_Number.py) | 1. Hash or set, O(n) and O(n)<br>2. xor O(n) and O(1) |
+| 137 | [Single Number II](https://leetcode.com/problems/single-number-ii/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/137_Single_Number_II.py) | 1. ctypes 32 % 3 and &, O(n) and O(1)<br>2. ones, twos, threes as bitmask (e.g. ones represents ith bit had appeared once), O(n) and O(1) | 
 | 138 | [Copy List with Random Pointer](https://leetcode.com/problems/copy-list-with-random-pointer/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/138_Copy_List_with_Random_Pointer.py) | 1. Hash O(n) and O(n)<br>2.  Modify original structure: Original->Copy->Original, then node.next.random = node.random.next, O(n) and O(1)|
 | 151 | [Reverse Words in a String](https://discuss.leetcode.com/category/159/reverse-words-in-a-string) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/151_Reverse_Words_in_a_String.py)| 1. Python split by space <br>2. Reverse all and reverse words |
 | 156 | [Binary Tree Upside Down](https://leetcode.com/problems/binary-tree-upside-down/) &hearts;| [Python](https://github.com/qiyuangong/leetcode/blob/master/python/156_Binary_Tree_Upside_Down.py) | p.left = parent.right, parent.right = p.right, p.right = parent, parent = p.left, p = left |

python/12_Integer_to_Roman.py

@@ -6,22 +6,40 @@
 #         """
 #
 class Solution(object):
+    # def intToRoman(self, num):
+    #     #http://www.rapidtables.com/convert/number/how-number-to-roman-numerals.htm
+    #     roman_dim = [[1000, 'M'], [900, 'CM'], [500, 'D'], [400, 'CD'],
+    #                  [100, 'C'], [90, 'XC'], [50, 'L'], [40, 'XL'], [10, 'X'],
+    #                  [9,'IX'], [5, 'V'], [4, 'IV'], [1, 'I']]
+    #     if num == 0:
+    #         return ''
+    #     roman_str = ''
+    #     current, dim = num, 0
+    #     while current != 0:
+    #         while current // roman_dim[dim][0] == 0:
+    #             dim += 1
+    #         while current - roman_dim[dim][0] >= 0:
+    #             current -= roman_dim[dim][0]
+    #             roman_str += roman_dim[dim][1]
+    #     return roman_str
+
     def intToRoman(self, num):
-        #http://www.rapidtables.com/convert/number/how-number-to-roman-numerals.htm
-        roman_dim = [[1000, 'M'], [900, 'CM'], [500, 'D'], [400, 'CD'],
-                     [100, 'C'], [90, 'XC'], [50, 'L'], [40, 'XL'], [10, 'X'],
-                     [9,'IX'], [5, 'V'], [4, 'IV'], [1, 'I']]
-        if num == 0:
-            return ''
-        roman_str = ''
-        current, dim = num, 0
-        while current != 0:
-            while current // roman_dim[dim][0] == 0:
-                dim += 1
-            while current - roman_dim[dim][0] >= 0:
-                current -= roman_dim[dim][0]
-                roman_str += roman_dim[dim][1]
-        return roman_str
+        values = [1000, 900, 500, 400,
+                  100, 90, 50, 40,
+                  10, 9, 5, 4, 1]
+        symbols = ["M", "CM", "D", "CD",
+                   "C", "XC", "L", "XL",
+                   "X", "IX", "V", "IV",
+                   "I"]
+        roman = ''
+        i = 0
+        while num > 0:
+            k = num / values[i]
+            for j in range(k):
+                roman += symbols[i]
+                num -= values[i]
+            i += 1
+        return roman
 
 if __name__ == '__main__':
     # begin

python/137_Single_Number_II.py

@@ -0,0 +1,31 @@
+class Solution(object):
+    # def singleNumber(self, nums):
+    #     """
+    #     :type nums: List[int]
+    #     :rtype: int
+    #     """
+    #     import ctypes
+    #     # note that if res is not c 32
+    #     # there will be errors
+    #     count = [0] * 32
+    #     res = ctypes.c_int32(0)
+    #     for i in range(32):
+    #         for num in nums:
+    #             if (ctypes.c_int32(num).value >> i) & 1:
+    #                 count[i] += 1
+    #         res.value |= ((count[i] % 3) << i)
+    #     return res.value
+
+    def singleNumber(self, nums):
+        # bitmask
+        # ones as a bitmask to represent the ith bit had appeared once.
+        # twos as a bitmask to represent the ith bit had appeared twice.
+        # threes as a bitmask to represent the ith bit had appeared three times.
+        ones, twos, threes = 0, 0, 0
+        for num in nums:
+            twos |= ones & num
+            ones ^= num
+            threes = ones & twos
+            ones &= ~threes
+            twos &= ~threes
+        return ones

python/13_Roman_to_Integer.py

@@ -1,26 +1,35 @@
-# class Solution(object):
-#     def romanToInt(self, s):
-#         """
-#         :type s: str
-#         :rtype: int
-#         """
-
 class Solution:
-    # @return an integer
+    # def romanToInt(self, s):
+    #     """
+    #     :type s: str
+    #     :rtype: int
+    #     """
+    #     roman = {'I': 1, 'V': 5, 'X': 10,
+    #              'L': 50, 'C': 100, 'D': 500, 'M': 1000}
+    #     result = 0
+    #     last = s[-1]
+    #     for t in reversed(s):
+    #         if t == 'C' and last in ['D', 'M']:
+    #             result -= roman[t]
+    #         elif t == 'X' and last in ['L', 'C']:
+    #             result -= roman[t]
+    #         elif t == 'I' and last in ['V', 'X']:
+    #             result -= roman[t]
+    #         else:
+    #             result += roman[t]
+    #         last = t
+    #     return result
+
     def romanToInt(self, s):
         roman = {'I': 1, 'V': 5, 'X': 10,
                  'L': 50, 'C': 100, 'D': 500, 'M': 1000}
-        result = 0
-        last = s[-1]
-        for t in reversed(s):
-            if t == 'C' and last in ['D', 'M']:
-                result -= roman[t]
-            elif t == 'X' and last in ['L', 'C']:
-                result -= roman[t]
-            elif t == 'I' and last in ['V', 'X']:
-                result -= roman[t]
-            else:
-                result += roman[t]
-            last = t
-        return result
+        prev, total = 0, 0
+        for c in s:
+            curr = roman[c]
+            total += curr
+            # need to subtract
+            if curr > prev:
+                total -= 2 * prev
+            prev = curr
+        return total