Implement longest common subsequence algorithm

krzysztof-grzybek · krzysztof-grzybek · commit b589f9bb6115 · 2016-12-23T21:35:36.000+01:00
diff --git a/src/searching/longest-common-subsequence.js b/src/searching/longest-common-subsequence.js
@@ -0,0 +1,44 @@
+(function (exports) {
+  'use strict';
+
+  exports.longestCommonSubsequence = (function () {
+
+    function getLcsLengths(str1, str2) {
+      var result = [];
+      for (var i = -1; i < str1.length; i = i + 1) {
+        result[i] = [];
+        for (var j = -1; j < str2.length; j = j + 1) {
+          if (i === -1 || j === -1) {
+            result[i][j] = 0;
+          } else if (str1[i] === str2[j]) {
+            result[i][j] = result[i - 1][j - 1] + 1;
+          } else {
+            result[i][j] = Math.max(result[i - 1][j], result[i][j - 1]);
+          }
+        }
+      }
+      return result;
+    }
+
+    function getLcs(str1, str2, lcsLengthsMatrix) {
+      var execute = function (i, j) {
+        if (!lcsLengthsMatrix[i][j]) {
+          return '';
+        } else if (str1[i] === str2[j]) {
+          return execute(i - 1, j - 1) + str1[i];
+        } else if (lcsLengthsMatrix[i][j - 1] > lcsLengthsMatrix[i - 1][j]) {
+          return execute(i, j - 1);
+        } else {
+          return execute(i - 1, j);
+        }
+      };
+      return execute(str1.length - 1, str2.length - 1);
+    }
+
+    return function (str1, str2) {
+      var lcsLengthsMatrix = getLcsLengths(str1, str2);
+      return getLcs(str1, str2, lcsLengthsMatrix);
+    };
+  })();
+
+})(typeof window === 'undefined' ? module.exports : window);
