diff --git a/hashmap/jewels-and-stones.js b/hashmap/jewels-and-stones.js
index 956bc44..0ff47ce 100644
--- a/hashmap/jewels-and-stones.js
+++ b/hashmap/jewels-and-stones.js
@@ -24,19 +24,19 @@ All the characters of jewels are unique.
  * @param {string} stones
  * @return {number}
  */
-var numJewelsInStones = function(jewels, stones) {
-    const map = {};
+var numJewelsInStones = function (jewels, stones) {
+  const map = {};
 
-    for (const jewel of jewels.split('')) {
-        map[jewel] = jewel;
-    }
+  for (const jewel of jewels.split("")) {
+    map[jewel] = jewel;
+  }
 
-    let counter = 0;
-    for (const stone of stones.split('')) {
-        if (map[stone]) {
-            counter++;
-        }
+  let counter = 0;
+  for (const stone of stones.split("")) {
+    if (map[stone]) {
+      counter++;
     }
+  }
 
-    return counter;
+  return counter;
 };
diff --git a/string/isomorphic-strings.js b/string/isomorphic-strings.js
new file mode 100644
index 0000000..54883df
--- /dev/null
+++ b/string/isomorphic-strings.js
@@ -0,0 +1,59 @@
+/**
+205. Isomorphic Strings
+
+Given two strings s and t, determine if they are isomorphic.
+
+Two strings s and t 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
+
+Constraints:
+1 <= s.length <= 5 * 104
+t.length == s.length
+s and t consist of any valid ascii character.
+*/
+
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {boolean}
+ */
+var isIsomorphic = function (s, t) {
+  const s2t = {};
+  const t2s = {};
+
+  for (let i = 0; i < s.length; i++) {
+    const sChar = s[i];
+    const tChar = t[i];
+
+    if (
+      (sChar in s2t && !(tChar in t2s)) ||
+      (tChar in t2s && !(sChar in s2t))
+    ) {
+      return false;
+    }
+
+    if (sChar in s2t && tChar in t2s) {
+      if (s2t[sChar] !== tChar || sChar !== t2s[tChar]) {
+        return false;
+      }
+    } else {
+      s2t[sChar] = tChar;
+      t2s[tChar] = sChar;
+    }
+  }
+
+  return true;
+};
diff --git a/string/swap-adjacent-in-lr-string.js b/string/swap-adjacent-in-lr-string.js
index ee66207..ad3f072 100644
--- a/string/swap-adjacent-in-lr-string.js
+++ b/string/swap-adjacent-in-lr-string.js
@@ -28,39 +28,39 @@ Both start and end will only consist of characters in 'L', 'R', and 'X'.
  * @param {string} end
  * @return {boolean}
  */
-var canTransform = function(start, end) {
-    const first  = [];
-    const second = [];
+var canTransform = function (start, end) {
+  const first = [];
+  const second = [];
 
-    for (let i = 0; i < start.length; i++){
-        if (start[i] !== 'X') {
-            first.push([i, start[i]]);
-        }
+  for (let i = 0; i < start.length; i++) {
+    if (start[i] !== "X") {
+      first.push([i, start[i]]);
     }
+  }
 
-    for (let j = 0; j < end.length; j++){
-        if(end[j] !== 'X') {
-            second.push([j, end[j]]);
-        }
+  for (let j = 0; j < end.length; j++) {
+    if (end[j] !== "X") {
+      second.push([j, end[j]]);
     }
+  }
 
-    if (first.length !== second.length ) {
-        return false;
-    }
+  if (first.length !== second.length) {
+    return false;
+  }
 
-    for (let i = 0; i < first.length; i++) {
-        if (first[i][1] !== second[i][1]) {
-            return false;
-        }
+  for (let i = 0; i < first.length; i++) {
+    if (first[i][1] !== second[i][1]) {
+      return false;
+    }
 
-        if (first[i][1] == 'L' && first[i][0] < second[i][0]) {
-            return false;
-        }
+    if (first[i][1] == "L" && first[i][0] < second[i][0]) {
+      return false;
+    }
 
-        if (first[i][1] == 'R' && first[i][0] > second[i][0]) {
-            return false;
-        }
+    if (first[i][1] == "R" && first[i][0] > second[i][0]) {
+      return false;
     }
+  }
 
-    return true;
+  return true;
 };