solution(python): 1220. Count Vowels Permutation

1220. Count Vowels Permutation
- Python

Hard/1220. Count Vowels Permutation/readme.md

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+Define a constant MOD to handle modular arithmetic to avoid integer overflow.
+
+Initialize five variables: countA, countE, countI, countO, and countU, each representing the count of valid strings of length 1 ending with the respective vowel ('a', 'e', 'i', 'o', 'u').
+
+Use a for loop to iterate from length = 1 to n - 1 because we already have the counts for length 1, and we want to calculate the counts for lengths 2 to n.
+
+Inside the loop, calculate the counts for each vowel for the next length based on the counts for the current length. The transitions are based on the given rules:
+
+countA for the next length is the count of strings ending with 'e'.
+countE for the next length is the count of strings ending with 'a' or 'i'.
+countI for the next length is the count of strings ending with 'a', 'e', 'o', or 'u'.
+countO for the next length is the count of strings ending with 'i' or 'u'.
+countU for the next length is the count of strings ending with 'a'.
+Update the variables countA, countE, countI, countO, and countU with the newly calculated counts for the next length.
+
+After the loop, the variables contain the counts of valid strings of length n ending with each vowel.
+
+Calculate the total count of valid strings for length n by summing up the counts for all vowels and take the result modulo MOD.
+
+Return the total count as an integer.
+
+The approach uses dynamic programming to efficiently compute the counts for different string lengths, following the rules for vowel transitions, and calculates the final result for length n.

Hard/1220. Count Vowels Permutation/solution.py

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+class Solution:
+    def countVowelPermutation(self, n: int) -> int:
+        MOD = 1000000007
+
+        # Initialize counts for each vowel for length 1
+        countA = 1
+        countE = 1
+        countI = 1
+        countO = 1
+        countU = 1
+
+        # Iterate from length 1 to n - 1
+        for length in range(1, n):
+            # Calculate the next counts for each vowel based on the previous counts
+            nextCountA = countE
+            nextCountE = (countA + countI) % MOD
+            nextCountI = (countA + countE + countO + countU) % MOD
+            nextCountO = (countI + countU) % MOD
+            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
+        totalCount = (countA + countE + countI + countO + countU) % MOD
+
+        return int(totalCount)