Feature dp implementation

include/0005_DynamicProgramming/0007_DecodeWays.h

@@ -0,0 +1,32 @@
+#pragma once
+
+#include<vector>
+#include<string>
+using namespace std;
+
+/*
+Pattern 1
+Linear Recurrence
+
+Description
+Let 1 maps to 'A', 2 maps to 'B', ..., 26 to 'Z'.Given a digit sequence, count the number of possible decodings of the given digit sequence.
+
+Consider the input string "123".There are three valid ways to decode it :
+"ABC" : The grouping is(1, 2, 3) -> 'A', 'B', 'C'
+"AW" : The grouping is(1, 23) -> 'A', 'W'
+"LC" : The grouping is(12, 3) -> 'L', 'C'
+Note : Groupings that contain invalid codes(e.g., "0" by itself or numbers greater than "26") are not allowed.
+For instance, the string "230" is invalid because "0" cannot stand alone, and "30" is greater than "26", so it cannot represent any letter.The task is to find the total number of valid ways to decode a given string.
+*/
+
+namespace DecodeWays
+{
+	class DynamicProgramming
+	{
+	private:
+		int CountWaysRecursiveHelper(string& digits, size_t index);
+	public:
+		int RecursiveCountWays(string digits);
+		int DpCountways(string digits);
+	};
+}

source/0005_DynamicProgramming/0007_DecodeWays.cc

@@ -0,0 +1,61 @@
+#include "../../include/0005_DynamicProgramming/0007_DecodeWays.h"
+
+namespace DecodeWays
+{
+	int DynamicProgramming::CountWaysRecursiveHelper(string& digits, size_t index)
+	{
+		size_t digitsLength = digits.size();
+
+		// Base case: If the end of the string is reached, return 1 as it signifies a valid decoding.
+		if (index >= digitsLength)
+		{
+			return 1;
+		}
+
+		int ways = 0;
+
+		// Single digit decoding: check if current digit is not '0'.
+		if (digits[index] != '0')
+		{
+			ways = this->CountWaysRecursiveHelper(digits, index + 1);
+		}
+
+		// Two digit decoding: check if next two digits are valid.
+		if ((index + 1 < digitsLength) && ((digits[index] == '1' && digits[index + 1] <= '9') || (digits[index] == '2' && digits[index + 1] <= '6')))
+		{
+			ways += this->CountWaysRecursiveHelper(digits, index + 2);
+		}
+		return ways;
+	}
+
+	int DynamicProgramming::RecursiveCountWays(string digits)
+	{
+		return this->CountWaysRecursiveHelper(digits, 0);
+	}
+
+	int DynamicProgramming::DpCountways(string digits)
+	{
+		size_t digitsLength = digits.size();
+
+		vector<int> dp(digitsLength + 1, 0);
+
+		dp[digitsLength] = 1;
+
+		for (int index = digitsLength - 1; index >= 0; index--)
+		{
+			// Single digit decoding: check if current digit is not '0'.
+			if (digits[index] != '0')
+			{
+				dp[index] = dp[index + 1];
+			}
+
+			// Two digit decoding: check if next two digits are valid.
+			if ((index + 1 < digitsLength) && ((digits[index] == '1' && digits[index + 1] <= '9') || (digits[index] == '2' && digits[index + 1] <= '6')))
+			{
+				dp[index] += dp[index + 2];
+			}
+		}
+
+		return dp[0];
+	}
+}

source/0005_DynamicProgramming/CMakeLists.txt

@@ -6,6 +6,7 @@ set(0005DYNAMICPROGRAMMING_SOURCES
     0004_MinimumCostClimbingStairs.cc
     0005_HouseRobber1.cc
     0006_HouseRobber2.cc
+    0007_DecodeWays.cc
 
 )
 

test/0005_DynamicProgramming/0007_DecodeWaysTest.cc

@@ -0,0 +1,47 @@
+#include<gtest/gtest.h>
+#include "../../include/0005_DynamicProgramming/0007_DecodeWays.h"
+
+namespace DecodeWays
+{
+	TEST(DecodeWays, RecursionTest01)
+	{
+		// Arrange
+		DynamicProgramming dp;
+		string digits = "121";
+		int expectedWaysCount = 3;
+
+		// Act
+		int actualWaysCount = dp.RecursiveCountWays(digits);
+
+		// Assert
+		ASSERT_EQ(expectedWaysCount, actualWaysCount);
+	}
+
+	TEST(DecodeWays, DpTest01)
+	{
+		// Arrange
+		DynamicProgramming dp;
+		string digits = "121";
+		int expectedWaysCount = 3;
+
+		// Act
+		int actualWaysCount = dp.DpCountways(digits);
+
+		// Assert
+		ASSERT_EQ(expectedWaysCount, actualWaysCount);
+	}
+
+	TEST(DecodeWays, DpTestInvalidInput)
+	{
+		// Arrange
+		DynamicProgramming dp;
+		string digits = "230";
+		int expectedWaysCount = 0;
+
+		// Act
+		int actualWaysCount = dp.DpCountways(digits);
+
+		// Assert
+		ASSERT_EQ(expectedWaysCount, actualWaysCount);
+	}
+}

test/0005_DynamicProgramming/CMakeLists.txt

@@ -20,6 +20,7 @@ add_executable(
   0004_MinimumCostClimbingStairsTest.cc
   0005_HouseRobber1Test.cc
   0006_HouseRobber2Test.cc
+  0007_DecodeWaysTest.cc
 
 )