feat: add No.205

Author: BaffinLee

201-300/205. Isomorphic Strings.md

@@ -0,0 +1,74 @@
+# 205. Isomorphic Strings
+
+- Difficulty: Easy.
+- Related Topics: Hash Table, String.
+- Similar Questions: Word Pattern.
+
+## Problem
+
+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.
+
+
+
+## Solution
+
+```javascript
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {boolean}
+ */
+var isIsomorphic = function(s, t) {
+    if (s.length !== t.length) return false;
+    var map = {};
+    var used = {};
+    for (var i = 0; i < s.length; i++) {
+        if (map[s[i]]) {
+            if (map[s[i]] !== t[i]) return false;
+        } else {
+            if (used[t[i]]) return false;
+            used[t[i]] = true;
+            map[s[i]] = t[i];
+        }
+    }
+    return true;
+};
+```
+
+**Explain:**
+
+nope.
+
+**Complexity:**
+
+* Time complexity : O(n).
+* Space complexity : O(n).