reorg and add code for second edition

11_dynamic_programming/javascript/01_longest_common_subsequence.js

@@ -0,0 +1,78 @@
+/**
+ * Search for LCS
+ *
+ * @param {string} string1 first string
+ * @param {string} string2 second string
+ *
+ * @return {object} with keys: lcs, offset, sequence
+ */
+function lcs(string1, string2) {
+	if (!string1 || !string2) {
+		return {
+			lcs: 0,
+			offset: 0,
+			sequence: ""
+		};
+	}
+
+	let lcs = 0;
+
+	let lastSubIndex = 0;
+
+	let table = [];
+	let len1 = string1.length;
+	let len2 = string2.length;
+	let row;
+	let col;
+
+	/**
+	 * Matrix
+	 * - has an increased dimension to avoid extra checks for previous elements
+	 *
+	 * - the number of rows is equal to the length of the first string + 1
+	 * - the number of columns is equal to the length of the second string + 1
+	 */
+	for (row = 0; row <= len1; row++) {
+		table[row] = [];
+		for (col = 0; col <= len2; col++) {
+			table[row][col] = 0;
+		}
+	}
+
+	// Fill the matrix
+	let i;
+	let j;
+
+	for (i = 0; i < len1; i++) {
+		for (j = 0; j < len2; j++) {
+			if (string1[i] === string2[j]) {
+				// The letters match
+				if (table[i][j] === 0) {
+					table[i + 1][j + 1] = 1;
+				} else {
+					table[i + 1][j + 1] = table[i][j] + 1;
+				}
+
+				// increment lcs if it's needed
+				if (table[i + 1][j + 1] > lcs) {
+					lcs = table[i + 1][j + 1];
+					lastSubIndex = i;
+				}
+			} else {
+				// The letters don't match
+				table[i + 1][j + 1] = 0;
+			}
+		}
+	}
+
+	return {
+		lcs: lcs,
+		offset: lastSubIndex - lcs + 1,
+		sequence: string1.slice(lastSubIndex - lcs + 1, lastSubIndex + 1)
+	};
+}
+
+console.log(lcs("hish", "fish")); // { lcs: 3, offset: 1, sequence: 'ish' }
+console.log(lcs("vista", "hish")); // { lcs: 2, offset: 1, sequence: 'is' }
+console.log(lcs("google", "abcdefgooglehijklm")); // { lcs: 6, offset: 0, sequence: 'google' }
+console.log(lcs("0", 0)); // { lcs: 0, offset: 0, sequence: '' }

11_dynamic_programming/javascript/02_levenstein.js

@@ -0,0 +1,47 @@
+/**
+ * Compute the edit distance between the two given strings
+ *
+ * @param {*} source
+ * @param {*} target
+ *
+ * @return {number}
+ */
+function getEditDistance(source, target) {
+	if (source.length == 0) return target.length;
+	if (target.length == 0) return source.length;
+
+	let i;
+	let j;
+	let matrix = [];
+
+	// Fill the column
+	for (i = 0; i <= target.length; i++) {
+		matrix[i] = [i];
+	}
+
+	// Fill the column
+	for (j = 0; j <= source.length; j++) {
+		matrix[0][j] = j;
+	}
+
+	// Fill in the rest of the matrix
+	for (i = 1; i <= target.length; i++) {
+		for (j = 1; j <= source.length; j++) {
+			if (target.charAt(i - 1) == source.charAt(j - 1)) {
+				matrix[i][j] = matrix[i - 1][j - 1];
+			} else {
+				matrix[i][j] = Math.min(
+					matrix[i - 1][j - 1] + 1, // substitution
+					Math.min(
+						matrix[i][j - 1] + 1, // insertion
+						matrix[i - 1][j] + 1
+					)
+				); // deletion
+			}
+		}
+	}
+
+	return matrix[target.length][source.length];
+}
+
+console.log(getEditDistance("google", "notgoogl")); // 4

11_dynamic_programming/javascript/examples/base.js

@@ -0,0 +1,7 @@
+module.exports = function initialize_matrix(rows, cols) {
+  let matrix = [];
+  for (let i = 0; i < rows.length; i++) {
+    matrix.push(Array(cols.length).fill(0));
+  }
+  return matrix;
+};

11_dynamic_programming/javascript/examples/diff_two_words.js

@@ -0,0 +1,25 @@
+const initialize_matrix = require("./base.js");
+
+function diff(firstWord, secondWord) {
+  let arr1 = firstWord.split("");
+  let arr2 = secondWord.split("");
+  let matrix = initialize_matrix(arr1, arr2);
+  for (let i = 0; i < arr1.length; i++) {
+    for (let j = 0; j < arr2.length; j++) {
+      if (arr1[i] == arr2[j]) {
+        if (i > 0 && j > 0) {
+          matrix[i][j] = matrix[i - 1][j - 1] + 1;
+        } else {
+          matrix[i][j] = 1;
+        }
+      } else {
+        if (i > 0 && j > 0) {
+          matrix[i][j] = Math.max(matrix[i - 1][j], matrix[i][j - 1]);
+        } else {
+          matrix[i][j] = 0;
+        }
+      }
+    }
+  }
+  return matrix[arr1.length - 1][arr2.length - 1];
+}