chore(CPlusPlus): added boyer moore for pattern searching (#512)

algorithms/CPlusPlus/README.md

@@ -101,6 +101,7 @@
 7. [Delete alternate characters in a string](Strings/delete-alternate-characters.cpp)
 8. [Print first letter of every word](Strings/print-first-letter.cpp)
 9. [Display longest name in a string array](Strings/longest-name.cpp)
+10. [Boyer Moore pattern search](Strings/Boyer_Moore.cpp)
 
 ## Trees
 

algorithms/CPlusPlus/Strings/Boyer_Moore.cpp

@@ -0,0 +1,87 @@
+/* C++ Program for Bad Character Heuristic of Boyer
+Moore String Matching Algorithm */
+#include <bits/stdc++.h>
+using namespace std;
+# define NO_OF_CHARS 256
+
+// The preprocessing function for Boyer Moore's
+// bad character heuristic
+void badCharHeuristic( string str, int size,
+						int badchar[NO_OF_CHARS])
+{
+	int i;
+
+	// Initialize all occurrences as -1
+	for (i = 0; i < NO_OF_CHARS; i++)
+		badchar[i] = -1;
+
+	// Fill the actual value of last occurrence
+	// of a character
+	for (i = 0; i < size; i++)
+		badchar[(int) str[i]] = i;
+}
+
+/* A pattern searching function that uses Bad
+Character Heuristic of Boyer Moore Algorithm */
+void search( string txt, string pat)
+{
+	int m = pat.size();
+	int n = txt.size();
+
+	int badchar[NO_OF_CHARS];
+
+	/* Fill the bad character array by calling
+	the preprocessing function badCharHeuristic()
+	for given pattern */
+	badCharHeuristic(pat, m, badchar);
+
+	int s = 0; // s is shift of the pattern with
+				// respect to text
+	while(s <= (n - m))
+	{
+		int j = m - 1;
+
+		/* Keep reducing index j of pattern while
+		characters of pattern and text are
+		matching at this shift s */
+		while(j >= 0 && pat[j] == txt[s + j])
+			j--;
+
+		/* If the pattern is present at current
+		shift, then index j will become -1 after
+		the above loop */
+		if (j < 0)
+		{
+			cout << "pattern occurs at shift = " << s << endl;
+
+			/* 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 */
+			s += (s + m < n)? m-badchar[txt[s + m]] : 1;
+
+		}
+
+		else
+			/* Shift the pattern so that the bad character
+			in text aligns with the last occurrence of
+			it in pattern. The max function is used to
+			make sure that we get a positive shift.
+			We may get a negative shift if the last
+			occurrence of bad character in pattern
+			is on the right side of the current
+			character. */
+			s += max(1, j - badchar[txt[s + j]]);
+	}
+}
+
+/* Driver code */
+int main()
+{
+	string txt= "ABAAABCD";
+	string pat = "ABC";
+	search(txt, pat);
+	return 0;
+}