diff --git a/day15/src/main.rs b/day15/src/main.rs
index 1501603..baf04a5 100644
--- a/day15/src/main.rs
+++ b/day15/src/main.rs
@@ -29,6 +29,13 @@ fn combine(ranges: &mut Vec<(i64, i64)>, l: i64, r: i64) {
             return;
         }
     }
+    if ranges.len() > 0 {
+        let (_, last_r) = ranges.last_mut().unwrap();
+        if l == *last_r + 1 {
+            *last_r = r;
+            return;
+        }
+    }       
     ranges.push((l, r));
 }
 
@@ -50,29 +57,27 @@ fn main() {
     println!("{:?}", sensors);
     println!("{:?}", beacons);
 
-    let target_y = &env::args().nth(2).expect("line").parse::<i64>().unwrap();
-    let mut coverage: Vec<(i64, i64)> = Vec::new();
-    for (sx, sy, range) in sensors {
-        let clip = (range as i64) - (sy - target_y).abs();
-        if clip < 0 {
-            continue;
-        }
-        let startx = sx - clip;
-        let endx = sx + clip;
-        combine(&mut coverage, startx, endx);
-         
-    }
-    println!("{:?}", coverage);
-
-    let mut sum = 0;
-    for (l, r) in coverage {
-        let mut overlap = 0;
-        for (bx, by) in &beacons {
-            if *by == *target_y && l <= *bx && r >= *bx {
-                overlap += 1;
+    let max_y = &env::args().nth(2).expect("max y").parse::<i64>().unwrap();
+    for target_y in 0..=*max_y {
+        let mut line_coverages: Vec<(i64, i64)> = Vec::new();
+        for (sx, sy, range) in &sensors {
+            let clip = (*range as i64) - (sy - target_y).abs();
+            if clip < 0 {
+                continue;
             }
+            let startx = sx - clip;
+            let endx = sx + clip;
+            line_coverages.push((startx, endx)); 
+        }
+        line_coverages.sort_by_key(|(x, _)| *x);
+        let mut coverage: Vec<(i64, i64)> = Vec::new();
+        for (startx, endx) in line_coverages {
+            combine(&mut coverage, startx, endx);
+        }
+        if coverage.len() > 1 {
+            let score = 4000000 * (coverage[0].1 + 1) + target_y;
+            println!("{:?} --> {:?}", coverage, score);
+            break;
         }
-        sum += r - l + 1 - overlap;
     }
-    println!("answer: {:?}", sum);
 }
diff --git a/day15/src/main1.rs b/day15/src/main1.rs
new file mode 100644
index 0000000..1501603
--- /dev/null
+++ b/day15/src/main1.rs
@@ -0,0 +1,78 @@
+use std::env;
+use std::fs::File;
+use std::io::{BufReader, BufRead};
+use std::cmp::{min, max};
+use std::collections::HashSet;
+
+fn parse_num(s: &[u8]) -> (i64, usize) {
+    let mut num: i64 = 0;
+    let negative = s[0] == '-' as u8;
+    let start = if negative {1} else {0};
+    let mut len = if negative {1} else {0};
+
+    for i in start..s.len() {
+        if s[i].is_ascii_digit() {
+            num = num*10 + (s[i] as i64 - '0' as i64);
+            len += 1;
+        } else {
+            break;
+        }
+    }
+    (if negative {-num} else {num}, len)
+}
+
+fn combine(ranges: &mut Vec<(i64, i64)>, l: i64, r: i64) {
+    for (l0, r0) in ranges.iter_mut() {
+        if *l0 <= r && l <= *r0 {
+            *l0 = min(*l0, l);
+            *r0 = max(*r0, r);
+            return;
+        }
+    }
+    ranges.push((l, r));
+}
+
+fn main() {
+    let file = File::open(&env::args().nth(1).expect("input")).expect("io err");
+    let lines = BufReader::new(file).lines();
+    let mut sensors: Vec<(i64, i64, u64)> = Vec::new();
+    let mut beacons: HashSet<(i64, i64)> = HashSet::new();
+    for line in lines.flatten() {
+        let l_bytes = line.as_bytes();
+        let (sx, e1) = parse_num(&l_bytes[12..]);
+        let (sy, e2) = parse_num(&l_bytes[12 + e1 + 4..]);
+        let (bx, e3) = parse_num(&l_bytes[12 + e1 + 4 + e2 + 25..]);
+        let (by, _) = parse_num(&l_bytes[12 + e1 + 4 + e2 + 25 + e3 + 4..]);
+        sensors.push((sx, sy, ((bx - sx).abs() + (by - sy).abs()) as u64));
+        beacons.insert((bx, by));
+    }
+    sensors.sort_by_key(|(x, _, _)| *x);
+    println!("{:?}", sensors);
+    println!("{:?}", beacons);
+
+    let target_y = &env::args().nth(2).expect("line").parse::<i64>().unwrap();
+    let mut coverage: Vec<(i64, i64)> = Vec::new();
+    for (sx, sy, range) in sensors {
+        let clip = (range as i64) - (sy - target_y).abs();
+        if clip < 0 {
+            continue;
+        }
+        let startx = sx - clip;
+        let endx = sx + clip;
+        combine(&mut coverage, startx, endx);
+         
+    }
+    println!("{:?}", coverage);
+
+    let mut sum = 0;
+    for (l, r) in coverage {
+        let mut overlap = 0;
+        for (bx, by) in &beacons {
+            if *by == *target_y && l <= *bx && r >= *bx {
+                overlap += 1;
+            }
+        }
+        sum += r - l + 1 - overlap;
+    }
+    println!("answer: {:?}", sum);
+}