Created boyerMoore.js

ayDavidGitHere · web-flow · commit e7cb578cb309 · 2022-04-20T22:37:11.000+01:00
Added boyerMoore string searching algorithm
diff --git a/String/boyerMoore.js b/String/boyerMoore.js
@@ -0,0 +1,58 @@
+  /**
+ *
+ * 
+ *Implementation of the Boyer-Moore String Search Algo.
+ *The Boyer–Moore string search algorithm allows linear time in
+ *      search by skipping 
+ *      indices when searching inside a string for a pattern. Fo
+ * 
+ *
+ * 
+ * 
+ * */
+let buildBadMatchTable = (str) => {
+    var tableObj = {},
+    strLength = str.length;
+    for (var i = 0; i < strLength - 1; i++) {
+        tableObj[str[i]] = strLength - 1 - i;
+    }
+    if (tableObj[str[strLength-1]] == undefined) {
+        tableObj[str[strLength-1]] = strLength;
+    }
+ return tableObj;
+}
+
+
+let boyerMoore = (str, pattern)=> {
+    var badMatchTable = buildBadMatchTable(pattern),
+    offset = 0,
+    patternLastIndex = pattern.length - 1,
+    scanIndex = patternLastIndex,
+    maxOffset = str.length - pattern.length;
+    // if the offset is bigger than maxOffset, cannot be found
+    while (offset <= maxOffset) {
+    scanIndex = 0;
+    while (pattern[scanIndex] == str[scanIndex + offset]) {
+    if (scanIndex == patternLastIndex) {
+    // found at this index
+        return offset;
+    }
+    scanIndex++;
+    }
+    var badMatchString = str[offset + patternLastIndex];
+    if (badMatchTable[badMatchString]) {
+    // increase the offset if it exists
+        offset += badMatchTable[badMatchString]
+    } else {
+        offset += 1;
+    }
+    }
+    return -1;
+}
+export {boyerMoore}
+
+
+
+
+
+
