From 5214edf75d2f3f0804a1758e39e85d4c95b94cbf Mon Sep 17 00:00:00 2001
From: Devon Sawatsky <devon@nove.dev>
Date: Wed, 19 Nov 2025 03:27:07 +0000
Subject: [PATCH] day4 part2

---
 src/lib.rs | 66 ++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 59 insertions(+), 7 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 6ad2c48..e5dbec1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -178,6 +178,58 @@ pub mod day4 {
         count.to_string()
     }
 
+    pub fn day4_part2(input: &str) -> String{
+        let input = string_to_array(input);
+        let mut count = 0;
+        for row in 1..input.len()-1 {
+            for col in 1..input.len()-1 {
+                if is_x_mas(&input, row, col) {
+                    count += 1;
+                }
+            }
+        }
+        count.to_string()
+    }
+
+    /* S&M combinations for X-MAS
+    MS
+    MS
+    
+    SM
+    SM
+
+    MM
+    SS
+
+    SS
+    MM */
+    //precondition: row and col are one away from the edge
+    fn is_x_mas(input: &Vec<Vec<char>>, row: usize, col: usize) -> bool {
+        if input[row][col] != 'A' {
+            return false;
+        }
+        if input[row-1][col-1] == 'M' {
+            if input[row-1][col+1] == 'M' {
+                input[row+1][col+1] == 'S' && input[row+1][col-1] == 'S'
+            } else if input[row+1][col-1] == 'M' {
+                input[row+1][col+1] == 'S' && input[row-1][col+1] == 'S'
+            } else {
+                false
+            }
+        } else if input[row-1][col-1] == 'S' {
+            if input[row-1][col+1] == 'S' {
+                input[row+1][col+1] == 'M' && input[row+1][col-1] == 'M'
+            } else if input[row+1][col-1] == 'S' {
+                input[row+1][col+1] == 'M' && input[row-1][col+1] == 'M'
+            } else {
+                false
+            }
+        } else {
+            false
+        }
+
+    }
+
     //squares only
     fn rotate_string_45degrees_counterclockwise(input: &str) -> String {
         let array_input = string_to_array(input);
@@ -305,13 +357,13 @@ mod tests {
         assert_eq!(result, "2493");
     }
 
-    // #[test]
-    // fn day4_part2_test() {
-    //     let test_result = day4::day4_part2(include_str!("../input/day4_part2.test.txt"));
-    //     assert_eq!(test_result, "48");
-    //     let result = day4::day4_part2(include_str!("../input/day4.txt"));
-    //     assert_eq!(result, "62098619");
-    // }
+    #[test]
+    fn day4_part2_test() {
+        let test_result = day4::day4_part2(include_str!("../input/day4.test.txt"));
+        assert_eq!(test_result, "9");
+        let result = day4::day4_part2(include_str!("../input/day4.txt"));
+        assert_eq!(result, "1890");
+    }
 
     #[test]
     fn day3_part1_test() {
-- 
2.51.2