7_Reverse_Integer.py

186_Reverse_Words_in_a_String_II

Author: qiyuangong

README.md

@@ -6,15 +6,17 @@
 
 | # | Title | Solution | Basic idea (One line) |
 |---| ----- | -------- | --------------------- |
-| 1 | [Two Sum](https://leetcode.com/problems/two-sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1_Two_Sum.py) | 1. hash O(n) and O(n) space<br>2. Sort and search with two points O(n) and O(1) space|
+| 1 | [Two Sum](https://leetcode.com/problems/two-sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1_Two_Sum.py) | 1. Hash O(n) and O(n) space<br>2. Sort and search with two points O(n) and O(1) space|
 | 3 | [Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/3_Longest_Substring_Without_Repeating_Characters.py) |1. Check every possible substring O(n^2) <br>2. Remember the character index and current check pos, if character index >= current pos, then there is duplicate |
 | 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 |
 | 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 |
 | 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 |
 | 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|
 | 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) |
 | 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|
@@ -23,4 +25,5 @@
 | 159 | [Longest Substring with At Most Two Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/159_Longest_Substring_with_At_Most_Two_Distinct_Characters.py) | Maintain a sliding window that always satisfies such condition |
 | 161 | [One Edit Distance](https://leetcode.com/problems/one-edit-distance/) &hearts;| [Python](https://github.com/qiyuangong/leetcode/blob/master/python/161_One_Edit_Distance.py) | 1. Check the different position and conditions<br>2. [Edit distance](https://leetcode.com/problems/edit-distance/)|
 | 163 | [Missing Ranges](https://leetcode.com/problems/missing-ranges/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/163_Missing_Ranges.py) | Add lower -1 for special case, then check if curr - prev >= 2|
+| 186 | [Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/) &hearts;| [Python](https://github.com/qiyuangong/leetcode/blob/master/python/186_Reverse_Words_in_a_String_II.py) | Reverse all and reverse each words |
 | 340 | [Longest Substring with At Most K Distinct Characters](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/340_Longest_Substring_with_At_Most_K_Distinct_Characters.py) | Maintain a sliding window with at most k distinct characters and a count for this window. Note that the start position need a loop to update.|

python/186_Reverse_Words_in_a_String_II.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def reverseWords(self, s):
+        """
+        :type s: a list of 1 length strings (List[str])
+        :rtype: nothing
+        """
+        ls, pos = len(s), 0
+        if s is None or ls == 0:
+            return
+        self.reverse(s, 0, ls)
+        for i in range(ls + 1):
+            if i == ls or s[i] == ' ':
+                self.reverse(s, pos, i)
+                pos = i + 1
+
+    def reverse(self, array_s, begin, end):
+        for i in range((end - begin) / 2):
+            array_s[begin + i], array_s[end - i - 1] = array_s[end - i - 1], array_s[begin + i]

python/7_Reverse_Integer.py

@@ -1,26 +1,39 @@
 class Solution:
     # @return an integer
 
+    # def reverse(self, x):
+    #     max_int = 2147483647
+    #     if x == 0:
+    #         return 0
+    #     isPos = True
+    #     if x < 0:
+    #         x *= (-1)
+    #         isPos = False
+    #     ltemp = []
+    #     while x != 0:
+    #         temp = x % 10
+    #         ltemp.append(temp)
+    #         x /= 10
+    #     result = 0
+    #     # the main solution
+    #     for t in ltemp:
+    #         result = result * 10 + t
+    #     if result > max_int:
+    #         result = 0
+    #     if isPos:
+    #         return result
+    #     else:
+    #         return -1 * result
+
     def reverse(self, x):
-        max_int = 2147483647
-        if x == 0:
-            return 0
-        isPos = True
+        # Note that in Python -1 / 10 = -1
+        res, isPos = 0, 1
         if x < 0:
-            x *= (-1)
-            isPos = False
-        ltemp = []
+            isPos = -1
+            x = -1 * x
         while x != 0:
-            temp = x % 10
-            ltemp.append(temp)
+            res = res * 10 + x % 10
+            if res > 2147483647:
+                return 0
             x /= 10
-        result = 0
-        for t in ltemp:
-            result = result * 10 + t
-        if result > max_int:
-            result = 0
-
-        if isPos:
-            return result
-        else:
-            return -1 * result
+        return res * isPos