Code style and 268_Missing_Number

Author: qiyuangong

README.md

@@ -89,6 +89,7 @@
 | 259 | [3Sum Smaller](https://leetcode.com/problems/3sum-smaller/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/259_3Sum_Smaller.py) | 1. Reduce to two sum smaller, then binary search, O(n^2lgn) and O(1)<br>2. Reduce to two sum smaller, then two points, O(n^2) and O(1)|
 | 266 | [Palindrome Permutation](https://leetcode.com/problems/palindrome-permutation/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/266_Palindrome_Permutation.py) | Compute frequency, check number of odd occurrences <= 1 then palindrome, O(n) and O(n)|
 | 267 | [Palindrome Permutation II](https://leetcode.com/problems/palindrome-permutation-ii/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/267_Palindrome_Permutation_II.py) | Check palindrome then generate half with [Permutations II](https://leetcode.com/problems/permutations-ii/), O(n^2) and O(n^2) |
+| 268 | [Missing Number](https://leetcode.com/problems/missing-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/268_Missing_Number.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/268_Missing_Number.java) | 1. Find missing by n * (n - 1)/2 - sum(nums)<br>2. XOR with index<br>3. Sort and binary search |
 | 270 | [Closest Binary Search Tree Value](https://leetcode.com/problems/closest-binary-search-tree-value/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/270_Closest_Binary_Search_Tree_Value.py) | 1. Recursively brute force, O(n) and O(n)<br>2. Recursively compare root result with current kid's result (left or right), O(logn) and O(logn)<br>3. Iteratively compare root result with current kid's result (left or right), O(logn) and O(logn) |
 | 274 | [H-Index](https://leetcode.com/problems/h-index/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/274_H-Index.py) | [Background](https://en.wikipedia.org/wiki/H-index)<br>1. Sort and check number of papers greater than h, O(nlogn) and O(1)<br>2. Counting sort, O(n) and O(n) |
 | 276 | [Paint Fence](https://leetcode.com/problems/paint-fence/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/276_Paint_Fence.py) | ways[i>2] = (ways[i-1] + ways[i-2]) * (k - 1), O(n) and O(1) |

java/268_Missing_Number.java

@@ -0,0 +1,30 @@
+class Solution {
+    /* public int missingNumber(int[] nums) {
+        int n = nums.length;
+        int total = n * (n + 1) / 2;
+        for (int i = 0; i < nums.length; i++) {
+            total -= nums[i];
+        }
+        return total;
+    } */
+
+    public int missingNumber(int[] nums) {
+        int res = nums.length;
+        for (int i = 0; i < nums.length; i++) {
+            res ^= i;
+            res ^= nums[i];
+        }
+        return res;
+    }
+
+    /* public int missingNumber(int[] nums) {
+        Arrays.sort(nums);
+        int left = 0, right = nums.length - 1;
+        while (left <= right) {
+            int mid = (left + right) / 2;
+            if (nums[mid] > mid) right = mid - 1;
+            else left = mid + 1;
+        }
+        return left;
+    } */
+}

java/367_Valid_Perfect_Square.java

@@ -31,4 +31,4 @@ public boolean isPerfectSquare(int num) {
         }
         return x * x == num;
     } */
-}
+}

java/387_First_Unique_Character_in_a_String.java

@@ -8,4 +8,4 @@ public int firstUniqChar(String s) {
                 return i;
         return -1;
     }
-}
+}

python/389_Find_the_Difference.java renamed to java/389_Find_the_Difference.java

@@ -14,4 +14,4 @@ public char findTheDifference(String s, String t) {
         }
         return (char) total;
     } */
-}
+}

python/268_Missing_Number.py

@@ -0,0 +1,26 @@
+class Solution(object):
+    # def missingNumber(self, nums):
+    #     """
+    #     :type nums: List[int]
+    #     :rtype: int
+    #     """
+    #     n = len(nums)
+    #     return (n ** 2 + n) / 2 - sum(nums)
+
+    def missingNumber(self, nums):
+        res = len(nums)
+        for i, v in enumerate(nums):
+            res ^= i
+            res ^= v
+        return res
+    
+    # def missingNumber(self, nums):
+    #     nums.sort()
+    #     left, right = 0, len(nums) - 1
+    #     while left <= right:
+    #         mid = (left + right) / 2
+    #         if nums[mid] <= mid:
+    #             left = mid + 1
+    #         else:
+    #             right = mid - 1
+    #     return left

python/388_Longest_Absolute_File_Path.py

@@ -21,4 +21,3 @@ def lengthLongestPath(self, input):
 if __name__ == '__main__':
     s = Solution()
     print s.lengthLongestPath("dir\n    file.txt")
-