Longest common sequences

Author: coderbean

src/main/java/nowcoder/LCS.java

@@ -0,0 +1,64 @@
+package nowcoder;
+
+import java.util.HashSet;
+import java.util.Scanner;
+import java.util.Set;
+
+/**
+ * Created by jacob on 2019-07-24.
+ */
+public class LCS {
+    public static void main(String[] args) {
+        LCS main = new LCS();
+        Scanner scanner = new Scanner(System.in);
+        while (scanner.hasNextLine()) {
+            String[] strings = scanner.nextLine().split(" ");
+            System.out.println(main.longestCommonSequence(strings[0], strings[1]));
+        }
+    }
+
+    private Set<String> longestCommonSequence(String a, String b) {
+        if (a.length() == 0 || b.length() == 0) {
+            return null;
+        }
+        int[][] dp = new int[a.length() + 1][b.length() + 1];
+        char[] aChars = a.toCharArray();
+        char[] bChars = b.toCharArray();
+        for (int i = 0; i < a.length(); i++) {
+            for (int j = 0; j < b.length(); j++) {
+                if (aChars[i] == bChars[j]) {
+                    dp[i + 1][j + 1] = dp[i][j] + 1;
+                } else {
+                    dp[i + 1][j + 1] = Math.max(dp[i][j + 1], dp[i + 1][j]);
+                }
+            }
+        } // 将二维数组的数据全部填充完毕
+
+        Set<String> result = new HashSet<>();
+        this.printCommonSequeue(aChars, bChars, dp, "", result, a.length(), b.length());
+        return result;
+    }
+
+    private void printCommonSequeue(char[] aChars, char[] bChars, int[][] dp,
+                                    String initStr, Set<String> result,
+                                    int i, int j) {
+        StringBuilder stringBuilder = new StringBuilder(initStr);
+        while (i > 0 && j > 0) {
+            if (aChars[i - 1] == bChars[j - 1]) {
+                stringBuilder.append(aChars[i - 1]);
+                i--;
+                j--;
+            } else {
+                if (dp[i][j - 1] > dp[i - 1][j]) {
+                    j--;
+                } else if (dp[i][j - 1] < dp[i - 1][j]) {
+                    i--;
+                } else {
+                    this.printCommonSequeue(aChars, bChars, dp, stringBuilder.toString(), result, i - 1, j);
+                    j--;
+                }
+            }
+        }
+        result.add(stringBuilder.reverse().toString());
+    }
+}

src/main/java/nowcoder/LCS2.java

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+package nowcoder;
+
+import java.util.Scanner;
+
+
+/**
+ * Created by jacob on 2019-07-24.
+ */
+public class LCS2 {
+    public static void main(String[] args) {
+        LCS2 main = new LCS2();
+        Scanner scanner = new Scanner(System.in);
+        while (scanner.hasNextLine()) {
+            String[] strings = scanner.nextLine().split(" ");
+            System.out.println(main.longestCommonSequence(strings[0], strings[1]));
+        }
+    }
+
+
+    private int longestCommonSequence(String a, String b) {
+        if (a.length() == 0 || b.length() == 0) {
+            return 0;
+        }
+        int[][] dp = new int[a.length() + 1][b.length() + 1];
+        char[] aChars = a.toCharArray();
+        char[] bChars = b.toCharArray();
+        for (int i = 0; i < a.length(); i++) {
+            for (int j = 0; j < b.length(); j++) {
+                if (aChars[i] == bChars[j]) {
+                    dp[i + 1][j + 1] = dp[i][j] + 1;
+                } else {
+                    dp[i + 1][j + 1] = Math.max(dp[i][j + 1], dp[i + 1][j]);
+                }
+            }
+        }
+        return dp[a.length()][b.length()];
+    }
+}