add 2405 ts solution

Author: JeremyXXXuuu

Problems/20-Optimal-Partition-of-String/2405.ts

@@ -0,0 +1,13 @@
+function partitionString(s: string): number {
+    let arr: string[] = [];
+    let count = 0;
+    for(let i = 0; i < s.length; i++) {
+        if(arr.indexOf(s[i])>= 0) {
+            count ++;
+            arr = [];
+        }
+        arr.push(s[i]);
+    }
+    return count+1;
+
+};