MoveHashToEnd

src/main/java/com/thealgorithms/twopointer/MoveHash.java

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+/**
+ * Moves all '#' characters to the end of the string.
+ *
+ * Time Complexity: O(n)
+ * Space Complexity: O(1)
+ *
+ * Inspired by Move Zeroes problem:
+ * https://leetcode.com/problems/move-zeroes/
+ *
+ * @author Shyam Chavda
+ */
+
+package com.thealgorithms.twopointer;
+
+public class MoveHash {
+
+    /** default constructor  */
+    public MoveHash() {}
+
+    /**
+     * Place all hash to end of the String and return new String.
+     *
+     * @param s the input string.
+     * @return the new string where hash place at the end.
+     * returns null if the input string is null.
+     */
+
+    public static String movehashtoend(String s) {
+        /** converts string into character array
+          for example.,
+               string = roman,
+               character array = ['r','o','m','a','n']
+         */
+
+        char[] c = s.toCharArray();
+
+        /** return null if inputed string is null */
+        if (s == null) {
+            return "null";
+        }
+
+        /** j works like a tracker the hash position */
+        int j = 0;
+
+        /** i traverse whole character array.
+         * if character is non-hash then easily swap with tracker(j) position
+         *
+         * for example.,
+         * input string = a#bc;
+         * at first traverse current non-hash character(a) swap with j position.
+         *
+         * string becomes #abc.
+         * this continuos untill i reaches to end of string.
+         */
+
+        for (int i=0; i<c.length; i++) {
+            if (c[i] != '#') {
+                swap(i, j, c);
+                j++;
+            }
+        }
+
+        /** converts the character array to String at a time and returns. */
+        return new String(c);
+    }
+
+    /** simple swapping logic with third variable. */
+    public static void swap(int a, int b, char[] c) {
+        char tmp = c[a];
+        c[a] = c[b];
+        c[b] = tmp;
+    }
+
+    public static void main(String[] args) {
+        /** input part. */
+        String input = "h#e#l###l#o";
+
+        /** output catches through the function.  */
+        String output = movehashtoend(input);
+
+        /** display appropriate output. */
+        System.out.println(output);
+    }
+}

src/test/java/com/thealgorithms/twopointer/MoveHashTest.java

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+package com.thealgorithms.twopointer;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class MoveHashTest {
+
+    @Test
+    void testMoveHash() {
+        assertEquals("hello#####", MoveHash.movehashtoend("h#e#l###l#o"));
+    }
+
+    @Test
+    void testEmpty() {
+        assertEquals("", MoveHash.movehashtoend(""));
+    }
+
+    @Test
+    void testNull() {
+        assertEquals(null, MoveHash.movehashtoend(null));
+    }
+}