922

Author: ProHiryu

TP/922.md

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+## 922 Sort Array By Parity II
+
+#### Description
+
+[link](https://leetcode.com/problems/sort-array-by-parity-ii/discuss/?currentPage=1&orderBy=most_votes&query=)
+
+---
+
+#### Solution
+
+- See Code
+
+---
+
+#### Code
+
+O(n)
+O(1)
+
+```python
+class Solution:
+    def sortArrayByParityII(self, a: List[int]) -> List[int]:
+        i = 0 # pointer for even misplaced
+        j = 1 # pointer for odd misplaced
+        sz = len(a)
+        
+        # invariant: for every misplaced odd there is misplaced even
+        # since there is just enough space for odds and evens
+
+        while i < sz and j < sz:
+            if a[i] % 2 == 0:
+                i += 2
+            elif a[j] % 2 == 1:
+                j += 2
+            else:
+                # a[i] % 2 == 1 AND a[j] % 2 == 0
+                a[i],a[j] = a[j],a[i]
+                i += 2
+                j += 2
+
+        return a   
+```