IsomorphicStrings: done

Author: rampatra

src/main/java/com/leetcode/maps/IsomorphicStrings.java

@@ -0,0 +1,104 @@
+package com.leetcode.maps;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Level: Easy
+ * Link: https://leetcode.com/problems/isomorphic-strings/
+ * Description:
+ * Given two strings s and t, determine if they are isomorphic.
+ *
+ * Two strings are isomorphic if the characters in s can be replaced to get t.
+ *
+ * All occurrences of a character must be replaced with another character while preserving the order of characters. No
+ * two characters may map to the same character but a character may map to itself.
+ *
+ * Example 1:
+ * Input: s = "egg", t = "add"
+ * Output: true
+ *
+ * Example 2:
+ * Input: s = "foo", t = "bar"
+ * Output: false
+ *
+ * Example 3:
+ * Input: s = "paper", t = "title"
+ * Output: true
+ *
+ * Note:
+ * You may assume both s and t have the same length.
+ *
+ * @author rampatra
+ * @since 2019-08-11
+ */
+public class IsomorphicStrings {
+
+    /**
+     * Time Complexity:
+     * Space Complexity:
+     * Runtime: <a href="https://leetcode.com/submissions/detail/250762080/">8 ms</a>.
+     *
+     * @param s
+     * @param t
+     * @return
+     */
+    public static boolean isIsomorphic(String s, String t) {
+
+        Map<Character, Character> sToTCharMap = new HashMap<>();
+        Map<Character, Character> tToSCharMap = new HashMap<>();
+
+        for (int i = 0; i < s.length(); i++) {
+            char chFromS = s.charAt(i);
+            char chFromT = t.charAt(i);
+            if (sToTCharMap.get(chFromS) == null && tToSCharMap.get(chFromT) == null) {
+                sToTCharMap.put(chFromS, chFromT);
+                tToSCharMap.put(chFromT, chFromS);
+            }
+            Character mappedChFromSToT = sToTCharMap.get(chFromS);
+            if (mappedChFromSToT == null || mappedChFromSToT != chFromT) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * Time Complexity:
+     * Space Complexity:
+     * Runtime: <a href="https://leetcode.com/submissions/detail/250761329/">3 ms</a>.
+     *
+     * @param s
+     * @param t
+     * @return
+     */
+    public static boolean isIsomorphicWithoutMaps(String s, String t) {
+        int[] charMap = new int[512];
+        for (int i = 0; i < s.length(); i++) {
+            char chFromS = s.charAt(i);
+            char chFromT = t.charAt(i);
+            if (charMap[chFromS] != charMap[chFromT + 256]) {
+                return false;
+            }
+            charMap[chFromS] = charMap[chFromT + 256] = i + 1;
+        }
+
+        return true;
+    }
+
+    public static void main(String[] args) {
+        assertTrue(isIsomorphic("egg", "add"));
+        assertFalse(isIsomorphic("foo", "bar"));
+        assertTrue(isIsomorphic("paper", "title"));
+        assertFalse(isIsomorphic("ab", "aa"));
+
+        assertTrue(isIsomorphicWithoutMaps("egg", "add"));
+        assertFalse(isIsomorphicWithoutMaps("foo", "bar"));
+        assertTrue(isIsomorphicWithoutMaps("paper", "title"));
+        assertFalse(isIsomorphicWithoutMaps("ab", "aa"));
+    }
+}