Added Boyer_Moore_Algorithm in Kotlin (#2813)

Boyer_Moore_Algorithm/Boyer_Moore.kt

@@ -0,0 +1,78 @@
+/*
+Boyer Moore String Matching Algorithm in Kotlin
+Author: Arkadip Bhattacharya (@darkmatter18)
+ */
+import java.util.*
+
+internal object Main {
+    private var NO_OF_CHARACTERS = 256
+    private fun maxOfAAndB(a: Int, b: Int): Int {
+        return a.coerceAtLeast(b)
+    }
+
+    private fun badCharacterHeuristic(str: CharArray, size: Int, badcharacter: IntArray) {
+
+        // Initialize all elements of bad character as -1
+        var i = 0
+        while (i < NO_OF_CHARACTERS) {
+            badcharacter[i] = -1
+            i++
+        }
+        // Fill the actual value of last occurrence of a character 
+        i = 0
+        while (i < size) {
+            badcharacter[str[i].toInt()] = i
+            i++
+        }
+    }
+
+    // A pattern searching function 
+    private fun search(text: CharArray, pattern: CharArray) {
+        val m = pattern.size
+        val n = text.size
+        val badCharacterHeuristic = IntArray(NO_OF_CHARACTERS)
+
+        // Fill the bad character array by calling the preprocessing function
+        badCharacterHeuristic(pattern, m, badCharacterHeuristic)
+
+        // s is shift of the pattern with respect to text
+        var s = 0
+        while (s <= n - m) {
+            var j = m - 1
+
+            // Keep reducing index j of pattern while characters of pattern and text are matching at this shift s
+            while (j >= 0 && pattern[j] == text[s + j]) j--
+
+            // If the pattern is present at current shift, then index j will become -1 after the above loop
+            s += if (j < 0) {
+                println("Patterns occur at shift = $s")
+
+                // Shift the pattern so that the next character in text aligns with the last occurrence of it in pattern. 
+                // The condition s+m < n is necessary for the case when pattern occurs at the end of text 
+                if (s + m < n) m - badCharacterHeuristic[text[s + m].toInt()] else 1
+            } else maxOfAAndB(1, j - badCharacterHeuristic[text[s + j].toInt()])
+        }
+    }
+
+    /* Driver program*/
+    @JvmStatic
+    fun main(args: Array<String>) {
+        val sc = Scanner(System.`in`)
+        var s = sc.nextLine()
+        val text = s.toCharArray()
+        s = sc.nextLine()
+        val pattern = s.toCharArray()
+        search(text, pattern)
+    }
+}
+
+/*
+Sample Input:
+AABAACAADAABAABA
+AABA
+
+Sample Output:
+Patterns occur at shift = 0
+Patterns occur at shift = 9
+Patterns occur at shift = 12
+ */