Leetcode | Count Number of Texts | Kotlin

devstromo · devstromo · commit 1863f5d80edf · 2025-05-04T19:18:38.000-03:00
diff --git a/leetcode/src/main/kotlin/com/devstromo/medium/p2266/1200px-telephone-keypad2svg.png b/leetcode/src/main/kotlin/com/devstromo/medium/p2266/1200px-telephone-keypad2svg.png
diff --git a/leetcode/src/main/kotlin/com/devstromo/medium/p2266/DESCRIPTION.md b/leetcode/src/main/kotlin/com/devstromo/medium/p2266/DESCRIPTION.md
@@ -0,0 +1,44 @@
+# 2266. Count Number of Texts
+
+Alice is texting Bob using her phone. The mapping of digits to letters is shown in the figure below.
+
+[Image](1200px-telephone-keypad2svg.png)
+
+In order to add a letter, Alice has to press the key of the corresponding digit i times, where i is the position of the
+letter in the key.
+
+- For example, to add the letter `'s'`, Alice has to press `'7'` four times. Similarly, to add the letter `'k'`, Alice
+  has to press `'5'` twice.
+- Note that the digits `'0'` and `'1'` do not map to any letters, so Alice does not use them.
+
+However, due to an error in transmission, Bob did not receive Alice's text message but received a string of pressed keys
+instead.
+
+- For example, when Alice sent the message `"bob"`, Bob received the string `"2266622"`.
+
+Given a string `pressedKeys` representing the string received by Bob, return the total number of possible text messages
+Alice could have sent.
+
+Since the answer may be very large, return it modulo `10^9 + 7`.
+
+Example 1:
+
+Input: pressedKeys = "22233"
+Output: 8
+Explanation:
+The possible text messages Alice could have sent are:
+"aaadd", "abdd", "badd", "cdd", "aaae", "abe", "bae", and "ce".
+Since there are 8 possible messages, we return 8.
+
+Example 2:
+
+Input: pressedKeys = "222222222222222222222222222222222222"
+Output: 82876089
+Explanation:
+There are 2082876103 possible text messages Alice could have sent.
+Since we need to return the answer modulo 109 + 7, we return 2082876103 % (109 + 7) = 82876089.
+
+Constraints:
+
+- `1 <= pressedKeys.length <= 10^5`
+- `pressedKeys` only consists of digits from `'2'` - `'9'`.
diff --git a/leetcode/src/main/kotlin/com/devstromo/medium/p2266/SolutionKt.kt b/leetcode/src/main/kotlin/com/devstromo/medium/p2266/SolutionKt.kt
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+package com.devstromo.medium.p2266
+
+class SolutionKt {
+    private val mod = 1_000_000_007
+
+    fun countTexts(pressedKeys: String): Int {
+        val n = pressedKeys.length
+        val dp = IntArray(n + 1)
+        dp[0] = 1
+
+        for (i in 1..n) {
+            val currentChar = pressedKeys[i - 1]
+            val maxPress = if (currentChar == '7' || currentChar == '9') 4 else 3
+
+            for (j in 1..maxPress) {
+                if (i - j < 0) break
+                if (pressedKeys[i - j] != currentChar) break
+                dp[i] = (dp[i] + dp[i - j]) % mod
+            }
+        }
+
+        return dp[n]
+    }
+}
diff --git a/leetcode/src/test/kotlin/com/devstromo/medium/p2266/SolutionKtUnitTest.kt b/leetcode/src/test/kotlin/com/devstromo/medium/p2266/SolutionKtUnitTest.kt
@@ -0,0 +1,14 @@
+package com.devstromo.medium.p2266
+
+import org.junit.jupiter.api.Assertions
+import org.junit.jupiter.api.Test
+
+class SolutionKtUnitTest {
+    private val solution = SolutionKt()
+
+    @Test
+    fun `Test Count Number of Texts`() {
+        Assertions.assertEquals(8, solution.countTexts("22233"))
+        Assertions.assertEquals(82876089, solution.countTexts("222222222222222222222222222222222222"))
+    }
+}
