diff --git a/src/day01.clj b/src/day01.clj
index ccc58c6..1b18548 100644
--- a/src/day01.clj
+++ b/src/day01.clj
@@ -63,50 +63,35 @@
                '("four" "4") '("five" "5") '("six" "6")
                '("seven" "7") '("eight" "8") '("nine" "9")])
 
-; the search tree
-; a node is a list with `:n` as first element, and then
-; many options list. Each list option is a (Char, Node|Leaf).
-; A leaf is (:l Int)
-
-; Tree :: Vec of Node | Leaf
-;
-; Node :: (Char, Tree)
-; Leaf :: String
-;
-; tree [
-;       (\a "1")
-;        ]
-;
+; Replaces the character at position `pos` with `replace`
 ;
+; string-replace-at :: String Int String -> String
+(defn string-replace-at [input pos replace]
+  (let [input-length (count input)
+        first-part (.substring input 0 pos)
+        second-part (.substring input (inc pos) input-length)]
+    (str first-part replace second-part)))
 
-; adds a new word to the current search tree
-(defn build-search-tree
-  ([] '())
-  ; (Tree, String, String) -> Tree
-  ([prev-tree new-word new-value]
-   (let
-     ; Vec of Char
-    [new-letters (sequence new-word)])))
-
-(defn new-leaf [value] value)
-(defn new-node [char tree] (list char tree))
-
-(def tree (new-node \a (new-leaf "A")))
-
-; (build-search-tree "a" "1")
-
-; Search tree that, given a starting index `idx`,
-; attempt to find a textual digit at that position.
-(defn digit-at? [letters idx])
-
-; Given "one3two4six" returns "13246"
-; Given "eighttwothree" should include "823" somewhere, in that order
-; String -> String
-(defn sanitize-str [input]
-  (reduce (fn [acc next] (clojure.string/replace acc (first next) (last next))) input patterns))
+; tests every character on every number
+(defn sanitize-2
+  "String -> String"
+  [input] (reduce (fn [acc str-pos]
+                    ; find which, if any, of the patterns matches on this pos
+                    ; match :: Maybe (String String)
+                    (let [match (utils/find-first (fn [pattern]
+                                                    (= str-pos (.indexOf acc (first pattern))))
+                                                  patterns)]
+                      ; if no number is found, return the acc as is,
+                      ; otherwise, replace the first character with the corresponding number
+                      (if (nil? match)
+                        acc
+                        ; replace the character at `str-pos` with the matched number
+                        (string-replace-at acc str-pos (last match)))))
+                  input
+                  (range (count input))))
 
 (defn part2 []
-  (let [sanitized-lines (map sanitize-str lines)
+  (let [sanitized-lines (map sanitize-2 lines)
         numbers-str (map calibration-value-1 sanitized-lines)
         numbers (map Integer/parseInt numbers-str)
         sum (reduce + 0 numbers)]
diff --git a/src/utils.clj b/src/utils.clj
index 636fc37..4e7787f 100644
--- a/src/utils.clj
+++ b/src/utils.clj
@@ -5,3 +5,7 @@
   ([day] (slurp (str "./input/" day ".txt")))
   ([day test?] (slurp (str "./input" (if test? "_test/" "/") day ".txt"))))
 
+(defn find-first
+  [f coll]
+  (first (filter f coll)))
+