coded + unit tested

Author: Ram swaroop

src/me/ramswaroop/strings/RemoveExtraSpaces.java

@@ -0,0 +1,59 @@
+package me.ramswaroop.strings;
+
+import java.util.Arrays;
+
+/**
+ * Created by IntelliJ IDEA.
+ *
+ * @author: ramswaroop
+ * @date: 10/25/15
+ * @time: 9:44 PM
+ */
+public class RemoveExtraSpaces {
+
+    /**
+     * Removes extra spaces in string {@param s} without creating a
+     * extra variable to hold the result, in O(n) time complexity.
+     *
+     * @param s
+     * @return
+     */
+    public static String removeExtraSpaces(String s) {
+        char[] c = s.toCharArray();
+
+        int j = c.length;
+        for (int i = 1; i < c.length; i++) {
+            // check for two or more consecutive spaces
+            if (c[i] == ' ' && c[i - 1] == ' ') {
+                // if extra spaces encountered for the 1st time
+                if (j == c.length) j = i;
+
+                // skip all extra spaces
+                while (i < c.length && c[i] == ' ') {
+                    i++;
+                }
+                
+                // if reached end of string then stop
+                if (i == c.length) break;
+            }
+
+            // copy characters occurring after extra spaces to their appropriate positions
+            while (i < c.length && j < c.length) {
+                if (c[i] == ' ' && c[i - 1] == ' ') break;
+
+                c[j] = c[i];
+                i++;
+                j++;
+            }
+        }
+
+        return String.valueOf(Arrays.copyOf(c, j));
+    }
+
+    public static void main(String a[]) {
+        System.out.println(removeExtraSpaces("ram swaroop is a good boy."));
+        System.out.println(removeExtraSpaces("ram swaroop      is      a    good boy."));
+        System.out.println(removeExtraSpaces("ram swaroop      is      a    good    boy    ."));
+        System.out.println(removeExtraSpaces("   ram swaroop      is      a    good boy    ."));
+    }
+}