Longest common substring & Edit distance added

AlgorithmCode/EditDistance.java

@@ -0,0 +1,68 @@
+/**
+ * An implementation of the edit distance algorithm
+ *
+ * <p>Time Complexity: O(nm)
+ *
+ * @author Micah Stairs
+*/
+
+public class EditDistance {
+
+ // Computes the cost to convert a string 'a' into a string 'b' using dynamic
+ // programming given the insertionCost, deletionCost and substitutionCost, O(nm)
+ public static int editDistance(
+ String a, String b, int insertionCost, int deletionCost, int substitutionCost) {
+
+ final int AL = a.length(), BL = b.length();
+ int[][] arr = new int[AL + 1][BL + 1];
+
+ for (int i = 0; i <= AL; i++) {
+ for (int j = (i == 0 ? 1 : 0); j <= BL; j++) {
+
+ int min = Integer.MAX_VALUE;
+
+ // Substitution
+ if (i > 0 && j > 0)
+ min = arr[i - 1][j - 1] + (a.charAt(i - 1) == b.charAt(j - 1) ? 0 : substitutionCost);
+
+ // Deletion
+ if (i > 0) min = Math.min(min, arr[i - 1][j] + deletionCost);
+
+ // Insertion
+ if (j > 0) min = Math.min(min, arr[i][j - 1] + insertionCost);
+
+ arr[i][j] = min;
+ }
+ }
+
+ return arr[AL][BL];
+ }
+
+ public static void main(String[] args) {
+
+ String a = "abcdefg";
+ String b = "abcdefg";
+
+ // The strings are the same so the cost is zero
+ System.out.println(editDistance(a, b, 10, 10, 10));
+
+ a = "aaa";
+ b = "aaabbb";
+
+ // 10*3 = 30 because of three insertions
+ System.out.println(editDistance(a, b, 10, 2, 3));
+
+ a = "1023";
+ b = "10101010";
+
+ // Outputs 2*2 + 4*5 = 24 for 2 substitutions and 4 insertions
+ System.out.println(editDistance(a, b, 5, 7, 2));
+
+ a = "923456789";
+ b = "12345";
+
+ // Outputs 4*4 + 1 = 16 because we need to delete 4
+ // characters and perform one substitution
+ System.out.println(editDistance(a, b, 2, 4, 1));
+ }
+}

AlgorithmCode/LongestCommonSubstring.java

@@ -0,0 +1,74 @@
+/**
+ * This file contains an implementation of finding the Longest Common Substring (LCS) between two
+ * strings using dynamic programming.
+ *
+ * <p>Time Complexity: O(nm)
+ *
+ * @author William Fiset, [email protected]
+ */
+
+public class LongestCommonSubstring {
+
+ // Returns a non unique Longest Common Substring
+ // between the strings str1 and str2 in O(nm)
+ public static String lcs(char[] A, char[] B) {
+
+ if (A == null || B == null) return null;
+
+ final int n = A.length;
+ final int m = B.length;
+
+ if (n == 0 || m == 0) return null;
+
+ int[][] dp = new int[n + 1][m + 1];
+
+ // Suppose A = a1a2..an-1an and B = b1b2..bn-1bn
+ for (int i = 1; i <= n; i++) {
+ for (int j = 1; j <= m; j++) {
+
+ // If ends match the LCS(a1a2..an-1an, b1b2..bn-1bn) = LCS(a1a2..an-1, b1b2..bn-1) + 1
+ if (A[i - 1] == B[j - 1]) dp[i][j] = dp[i - 1][j - 1] + 1;
+
+ // If the ends do not match the LCS of a1a2..an-1an and b1b2..bn-1bn is
+ // max( LCS(a1a2..an-1, b1b2..bn-1bn), LCS(a1a2..an-1an, b1b2..bn-1) )
+ else dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
+ }
+ }
+
+ int lcsLen = dp[n][m];
+ char[] lcs = new char[lcsLen];
+ int index = 0;
+
+ // Backtrack to find a LCS. We search for the cells
+ // where we included an element which are those with
+ // dp[i][j] != dp[i-1][j] and dp[i][j] != dp[i][j-1])
+ int i = n, j = m;
+ while (i >= 1 && j >= 1) {
+
+ int v = dp[i][j];
+
+ // The order of these may output different LCSs
+ while (i > 1 && dp[i - 1][j] == v) i--;
+ while (j > 1 && dp[i][j - 1] == v) j--;
+
+ // Make sure there is a match before adding
+ if (v > 0) lcs[lcsLen - index++ - 1] = A[i - 1]; // or B[j-1];
+
+ i--;
+ j--;
+ }
+
+ return new String(lcs, 0, lcsLen);
+ }
+
+ public static void main(String[] args) {
+
+ char[] A = {'A', 'X', 'B', 'C', 'Y'};
+ char[] B = {'Z', 'A', 'Y', 'W', 'B', 'C'};
+ System.out.println(lcs(A, B)); // ABC
+
+ A = new char[] {'3', '9', '8', '3', '9', '7', '9', '7', '0'};
+ B = new char[] {'3', '3', '9', '9', '9', '1', '7', '2', '0', '6'};
+ System.out.println(lcs(A, B)); // 339970
+ }
+}

ProblemSolvingCodeBOJ/CodingQuestion17_11.java

@@ -44,6 +44,8 @@ public static void check(Point dot1, Point dot2) {
  public static void main(String[] args) {
  dot1();
  System.out.println(max);
+ //Output:
+ // 9
  }
 
  static class Point {