Update README_EN.md

Added an optimized O(n) time complexity and O(1) Space Complexity.

Author: iancarson

solution/1200-1299/1220.Count Vowels Permutation/README_EN.md

@@ -214,7 +214,39 @@ class Solution {
     }
 }
 ```
+```Java(Optimized with O(n) Time Complexity and O(1) Space)
+class Solution {
+    private final int mod = (int) 1e9 + 7;
+
+    public int countVowelPermutation(int n) {
+        final int MOD = 1000000007;
+        
+        long countA = 1, countE = 1, countI = 1, countO = 1, countU = 1;
+        
+        for (int length = 1; length < n; length++) {
+            // Calculate the next counts for each vowel based on the previous counts
+            long nextCountA = countE;
+            long nextCountE = (countA + countI) % MOD;
+            long nextCountI = (countA + countE + countO + countU) % MOD;
+            long nextCountO = (countI + countU) % MOD;
+            long nextCountU = countA;
+            
+            // Update the counts with the newly calculated values for the next length
+            countA = nextCountA;
+            countE = nextCountE;
+            countI = nextCountI;
+            countO = nextCountO;
+            countU = nextCountU;
+        }
+        
+        // Calculate the total count of valid strings for length n
+        long totalCount = (countA + countE + countI + countO + countU) % MOD;
+        
+        return (int) totalCount;
+    }
 
+}
+```
 ### **C++**
 
 ```cpp