Added string pattern matching algorithm (TheAlgorithms#238)

thivagar-manickam · web-flow · commit f530f816afaa · 2020-08-19T12:02:22.000+05:30
diff --git a/String/PatternMatching.js b/String/PatternMatching.js
@@ -0,0 +1,36 @@
+/*
+Pattern matching is case insensitive as
+the inputs are converted to lower case before the
+algorithm is run.
+
+The algorithm will run through the entire text and
+return the starting index if the given pattern is
+available in the text
+*/
+const checkIfPatternExists = (text, pattern) => {
+  const textLength = text.length // Store the length of the text in a variable
+  const patternLength = pattern.length // Store the length of the pattern in a variable
+
+  // Iterate through the text until the textlength - patternlength index
+  for (let i = 0; i <= textLength - patternLength; i++) {
+    // For each character in the text check if the subsequent character
+    // are matching the given pattern; if not break from the condition
+    for (let j = 0; j < textLength; j++) {
+      if (text[i + j] !== pattern[j]) break
+
+      // For each iteration of j check if the value of
+      // j + 1 is equal to the length of the pattern
+      if (j + 1 === patternLength) {
+        console.log(`Given pattern is found at index ${i}`)
+      }
+    }
+  }
+}
+
+const main = () => {
+  const text = 'AABAACAADAABAAAABAA'
+  const pattern = 'AABA'
+  checkIfPatternExists(text.toLowerCase(), pattern.toLowerCase())
+}
+
+main()
