diff --git a/data/day5a.txt b/data/day5a.txt
new file mode 100644
index 0000000..d7b445a
--- /dev/null
+++ b/data/day5a.txt
@@ -0,0 +1,500 @@
+593,10 -> 593,98
+777,236 -> 964,236
+650,575 -> 476,575
+120,612 -> 715,17
+508,707 -> 508,89
+98,834 -> 751,834
+623,554 -> 623,701
+929,976 -> 62,109
+368,893 -> 330,931
+495,335 -> 40,335
+44,704 -> 423,704
+683,711 -> 683,487
+26,940 -> 833,133
+961,183 -> 454,183
+301,306 -> 301,935
+973,822 -> 398,822
+639,911 -> 515,911
+861,180 -> 184,857
+31,97 -> 857,923
+966,376 -> 966,114
+881,485 -> 881,377
+930,98 -> 110,918
+841,889 -> 841,35
+512,261 -> 880,261
+48,533 -> 48,674
+207,226 -> 52,226
+823,952 -> 177,306
+331,566 -> 423,566
+422,418 -> 422,130
+699,517 -> 699,567
+757,784 -> 241,784
+508,445 -> 560,393
+866,275 -> 435,706
+74,41 -> 74,258
+386,369 -> 334,317
+240,94 -> 240,969
+851,197 -> 577,197
+28,906 -> 741,193
+286,227 -> 286,293
+849,800 -> 849,665
+736,307 -> 336,307
+69,701 -> 494,276
+421,823 -> 96,823
+121,626 -> 121,393
+318,351 -> 194,351
+670,671 -> 439,671
+603,914 -> 603,272
+61,507 -> 61,889
+266,39 -> 157,39
+543,664 -> 869,664
+382,709 -> 884,709
+499,80 -> 548,80
+489,79 -> 878,79
+695,86 -> 644,86
+987,585 -> 987,557
+287,67 -> 551,67
+975,983 -> 35,43
+707,351 -> 232,351
+529,175 -> 852,175
+32,811 -> 604,811
+106,153 -> 815,153
+195,268 -> 509,582
+50,922 -> 312,922
+220,500 -> 872,500
+473,33 -> 569,33
+858,847 -> 162,151
+937,947 -> 26,36
+726,435 -> 402,435
+686,601 -> 474,813
+764,880 -> 84,200
+850,950 -> 850,464
+413,620 -> 413,285
+893,560 -> 229,560
+149,100 -> 149,901
+358,613 -> 243,613
+202,445 -> 202,411
+127,153 -> 513,539
+147,846 -> 53,940
+139,920 -> 679,380
+913,953 -> 913,735
+339,466 -> 339,177
+113,882 -> 647,882
+18,880 -> 134,880
+897,152 -> 897,428
+473,511 -> 636,511
+880,370 -> 358,370
+400,244 -> 721,244
+419,987 -> 120,688
+872,224 -> 481,224
+335,302 -> 730,302
+961,324 -> 961,157
+769,301 -> 959,301
+829,124 -> 144,124
+523,372 -> 985,372
+520,33 -> 520,685
+554,644 -> 808,898
+82,676 -> 870,676
+303,612 -> 303,705
+338,40 -> 338,939
+836,47 -> 72,811
+371,751 -> 575,955
+929,505 -> 929,324
+273,181 -> 275,183
+347,595 -> 347,463
+95,629 -> 95,606
+809,188 -> 126,871
+857,924 -> 145,212
+668,277 -> 668,63
+700,904 -> 700,45
+814,899 -> 22,899
+205,98 -> 714,607
+943,28 -> 40,931
+282,620 -> 773,129
+424,803 -> 285,803
+688,329 -> 299,329
+146,628 -> 34,628
+573,417 -> 164,826
+292,232 -> 412,112
+412,508 -> 145,508
+632,648 -> 632,92
+885,904 -> 885,513
+295,981 -> 132,818
+134,681 -> 41,681
+810,531 -> 959,531
+188,590 -> 188,215
+960,795 -> 189,24
+729,211 -> 729,833
+214,817 -> 845,817
+196,609 -> 584,609
+384,908 -> 384,101
+770,907 -> 770,530
+451,469 -> 451,812
+571,261 -> 834,261
+799,436 -> 799,983
+248,105 -> 248,879
+783,906 -> 783,903
+955,670 -> 790,670
+723,750 -> 723,429
+572,427 -> 546,427
+610,341 -> 527,341
+925,426 -> 816,317
+151,403 -> 151,684
+408,969 -> 408,369
+276,425 -> 276,75
+186,86 -> 186,758
+412,420 -> 412,531
+361,60 -> 976,60
+787,649 -> 667,769
+45,866 -> 91,866
+319,963 -> 51,963
+112,866 -> 112,747
+291,475 -> 504,475
+175,116 -> 357,116
+968,961 -> 968,213
+13,12 -> 987,986
+640,728 -> 767,728
+981,505 -> 246,505
+864,981 -> 128,981
+91,66 -> 931,906
+798,116 -> 91,823
+552,74 -> 88,538
+620,872 -> 232,872
+45,229 -> 658,229
+413,75 -> 413,436
+815,257 -> 815,686
+989,22 -> 36,975
+178,904 -> 233,849
+635,128 -> 635,96
+640,820 -> 640,313
+890,787 -> 167,64
+221,22 -> 826,22
+914,132 -> 60,986
+848,31 -> 392,487
+105,969 -> 858,969
+903,868 -> 143,108
+38,941 -> 621,358
+171,340 -> 14,497
+286,460 -> 81,255
+726,688 -> 857,819
+494,689 -> 510,689
+517,913 -> 598,913
+932,66 -> 932,431
+977,982 -> 18,23
+95,101 -> 95,278
+574,467 -> 349,467
+63,803 -> 63,882
+838,874 -> 255,874
+900,752 -> 181,33
+102,897 -> 989,10
+374,439 -> 374,277
+513,504 -> 513,885
+814,932 -> 814,407
+824,656 -> 959,521
+415,570 -> 616,570
+577,880 -> 577,181
+287,524 -> 986,524
+955,665 -> 323,665
+556,365 -> 263,658
+154,226 -> 886,226
+803,750 -> 866,750
+558,725 -> 558,395
+941,115 -> 941,150
+180,410 -> 180,874
+458,753 -> 112,753
+199,253 -> 363,253
+423,650 -> 22,650
+892,851 -> 279,238
+611,109 -> 611,198
+983,344 -> 339,988
+299,47 -> 299,934
+435,652 -> 700,387
+186,775 -> 677,284
+136,576 -> 136,368
+818,744 -> 305,744
+767,171 -> 767,431
+930,842 -> 259,171
+342,831 -> 342,601
+193,672 -> 46,525
+925,164 -> 528,164
+725,92 -> 617,200
+67,729 -> 67,739
+547,153 -> 547,245
+763,434 -> 763,509
+314,888 -> 357,888
+72,645 -> 491,645
+92,67 -> 240,67
+827,936 -> 788,897
+852,378 -> 77,378
+448,337 -> 668,337
+846,739 -> 499,739
+465,691 -> 315,541
+716,163 -> 18,861
+78,965 -> 983,60
+114,952 -> 820,246
+950,351 -> 419,882
+266,36 -> 266,482
+773,841 -> 773,66
+742,198 -> 742,46
+417,512 -> 304,625
+900,277 -> 900,338
+983,431 -> 473,941
+986,282 -> 734,30
+742,19 -> 769,19
+952,320 -> 948,324
+92,590 -> 548,590
+107,39 -> 107,696
+603,749 -> 603,26
+55,282 -> 888,282
+670,848 -> 985,533
+981,982 -> 92,93
+147,428 -> 649,930
+773,737 -> 821,785
+791,576 -> 791,852
+327,672 -> 530,469
+847,122 -> 381,122
+419,493 -> 498,572
+879,842 -> 879,239
+267,717 -> 267,869
+142,449 -> 174,417
+342,718 -> 342,397
+603,207 -> 314,207
+612,648 -> 735,771
+37,10 -> 971,944
+891,716 -> 891,86
+252,217 -> 662,627
+185,165 -> 941,921
+854,717 -> 676,717
+158,791 -> 336,791
+762,226 -> 98,890
+73,189 -> 92,189
+649,511 -> 253,115
+719,456 -> 514,251
+605,286 -> 325,286
+454,609 -> 454,489
+374,541 -> 783,541
+599,177 -> 94,682
+600,384 -> 32,384
+810,933 -> 39,162
+780,871 -> 409,871
+24,639 -> 24,316
+454,80 -> 454,95
+556,541 -> 907,541
+627,295 -> 750,295
+245,71 -> 214,102
+725,445 -> 614,445
+779,538 -> 779,390
+746,667 -> 351,272
+117,776 -> 117,660
+498,495 -> 88,905
+697,721 -> 697,919
+580,314 -> 580,166
+22,656 -> 641,37
+413,433 -> 44,802
+182,305 -> 805,928
+739,277 -> 739,499
+172,210 -> 172,259
+894,576 -> 894,322
+265,263 -> 265,437
+430,228 -> 780,578
+464,531 -> 798,531
+713,63 -> 668,63
+918,831 -> 256,169
+414,375 -> 467,375
+440,32 -> 391,32
+439,806 -> 955,806
+335,820 -> 335,279
+727,458 -> 422,458
+312,274 -> 619,581
+136,724 -> 538,322
+589,680 -> 589,850
+335,648 -> 232,545
+499,216 -> 405,216
+942,710 -> 942,455
+969,556 -> 721,556
+756,552 -> 756,902
+98,870 -> 445,870
+476,833 -> 476,269
+820,127 -> 407,127
+337,519 -> 714,519
+756,95 -> 11,840
+317,339 -> 317,286
+353,86 -> 43,86
+93,950 -> 938,105
+705,509 -> 705,319
+244,879 -> 721,402
+434,794 -> 711,517
+272,381 -> 431,381
+652,104 -> 652,587
+850,866 -> 34,50
+645,902 -> 79,336
+701,39 -> 701,295
+492,793 -> 95,396
+352,554 -> 395,554
+123,405 -> 322,206
+941,745 -> 716,520
+450,512 -> 569,631
+42,25 -> 817,800
+909,387 -> 909,863
+919,934 -> 919,546
+439,881 -> 569,881
+167,866 -> 167,669
+242,264 -> 242,694
+981,786 -> 228,33
+452,434 -> 452,660
+22,26 -> 22,29
+26,155 -> 677,806
+801,627 -> 313,627
+657,135 -> 657,270
+872,875 -> 440,443
+636,248 -> 636,338
+776,51 -> 93,51
+498,600 -> 894,600
+263,984 -> 263,807
+416,390 -> 899,873
+269,137 -> 976,137
+752,12 -> 752,617
+55,925 -> 548,925
+856,551 -> 771,551
+653,93 -> 653,587
+403,286 -> 403,417
+895,706 -> 221,32
+139,822 -> 139,928
+696,194 -> 696,143
+270,678 -> 710,678
+879,353 -> 879,360
+949,712 -> 752,712
+665,661 -> 817,661
+462,952 -> 980,434
+692,766 -> 692,478
+157,117 -> 144,117
+438,701 -> 408,701
+401,703 -> 401,724
+876,831 -> 108,63
+749,892 -> 832,892
+455,124 -> 455,776
+551,222 -> 551,372
+533,80 -> 726,80
+342,740 -> 56,740
+793,370 -> 34,370
+949,614 -> 949,623
+610,287 -> 610,760
+978,834 -> 85,834
+644,894 -> 644,341
+35,887 -> 176,887
+168,958 -> 964,162
+341,886 -> 341,470
+417,845 -> 417,702
+338,347 -> 304,313
+651,10 -> 72,10
+853,160 -> 853,85
+381,568 -> 436,623
+794,437 -> 250,437
+861,72 -> 206,72
+807,813 -> 807,827
+820,502 -> 820,329
+547,508 -> 547,773
+160,129 -> 160,175
+756,468 -> 756,80
+442,661 -> 405,661
+304,817 -> 304,765
+99,42 -> 957,900
+212,110 -> 854,752
+44,620 -> 661,620
+212,311 -> 784,883
+329,671 -> 329,908
+86,359 -> 553,826
+257,799 -> 934,122
+409,663 -> 409,367
+528,623 -> 593,688
+957,525 -> 544,938
+846,766 -> 113,33
+176,680 -> 176,102
+167,287 -> 167,929
+932,870 -> 834,968
+86,774 -> 49,774
+745,231 -> 70,906
+435,760 -> 138,463
+776,810 -> 625,810
+928,930 -> 76,78
+602,24 -> 602,688
+394,424 -> 65,424
+946,966 -> 93,113
+494,39 -> 951,39
+607,699 -> 832,699
+13,403 -> 391,403
+726,475 -> 726,29
+828,625 -> 836,617
+396,770 -> 167,770
+28,546 -> 374,200
+56,113 -> 837,894
+290,589 -> 740,139
+930,805 -> 296,171
+646,895 -> 49,895
+111,15 -> 111,497
+11,274 -> 570,833
+257,624 -> 603,624
+63,844 -> 666,844
+846,661 -> 846,464
+431,72 -> 431,674
+726,674 -> 726,40
+286,660 -> 286,909
+847,222 -> 847,861
+325,896 -> 325,416
+793,953 -> 365,953
+987,956 -> 62,31
+845,853 -> 363,371
+79,782 -> 506,782
+424,21 -> 424,369
+938,162 -> 177,923
+86,193 -> 799,906
+320,164 -> 320,654
+840,306 -> 840,711
+852,736 -> 852,690
+876,966 -> 143,233
+787,926 -> 38,177
+374,112 -> 340,112
+132,541 -> 740,541
+29,28 -> 968,967
+916,212 -> 170,958
+371,553 -> 521,403
+88,796 -> 870,796
+656,367 -> 71,367
+785,166 -> 785,427
+320,30 -> 320,549
+909,527 -> 816,620
+832,965 -> 302,965
+672,259 -> 80,259
+578,513 -> 578,243
+975,561 -> 537,123
+135,330 -> 188,330
+501,695 -> 501,573
+717,230 -> 878,230
+854,501 -> 27,501
+705,885 -> 950,885
+704,338 -> 704,630
+477,485 -> 864,485
+901,42 -> 305,638
+660,540 -> 660,546
+555,79 -> 190,79
+226,126 -> 800,700
+575,908 -> 944,908
+94,478 -> 94,746
+461,425 -> 929,893
+861,429 -> 451,19
+832,825 -> 179,172
+186,133 -> 298,133
+684,270 -> 558,270
+786,872 -> 125,872
+649,178 -> 649,595
+893,738 -> 412,257
+760,854 -> 901,713
+16,914 -> 866,64
+935,928 -> 266,259
+323,229 -> 32,229
+608,828 -> 608,49
+715,892 -> 74,251
+787,187 -> 787,903
+405,793 -> 405,183
+232,704 -> 232,389
+130,706 -> 130,657
diff --git a/data/day5t.txt b/data/day5t.txt
new file mode 100644
index 0000000..1d4e36d
--- /dev/null
+++ b/data/day5t.txt
@@ -0,0 +1,10 @@
+0,9 -> 5,9
+8,0 -> 0,8
+9,4 -> 3,4
+2,2 -> 2,1
+7,0 -> 7,4
+6,4 -> 2,0
+0,9 -> 2,9
+3,4 -> 1,4
+0,0 -> 8,8
+5,5 -> 8,2
\ No newline at end of file
diff --git a/src/bin/day5.rs b/src/bin/day5.rs
new file mode 100644
index 0000000..ab017c8
--- /dev/null
+++ b/src/bin/day5.rs
@@ -0,0 +1,273 @@
+use advent2021::from_file_data;
+use core::cmp;
+use std::num::ParseIntError;
+use std::str::FromStr;
+use thiserror::Error;
+
+#[cfg(test)]
+const TEST_DATA: &str = include_str!("../../data/day5t.txt");
+const DAY5_DATA: &str = include_str!("../../data/day5a.txt");
+
+#[derive(Debug, Error, PartialEq)]
+enum Oopsie {
+    #[error("Couldn't parse number: {0}")]
+    BadNumber(#[from] ParseIntError),
+    #[error("Couldn't parse a point")]
+    InvalidPoint,
+    #[error("Couldn't parse a segment")]
+    InvalidSegment,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+struct Point {
+    x: usize,
+    y: usize,
+}
+
+impl FromStr for Point {
+    type Err = Oopsie;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.split_once(',') {
+            None => Err(Oopsie::InvalidPoint),
+            Some((xstr, ystr)) => {
+                let x = usize::from_str(xstr)?;
+                let y = usize::from_str(ystr)?;
+
+                Ok(Point { x, y })
+            }
+        }
+    }
+}
+
+#[test]
+fn basic_point_parsing() {
+    assert_eq!(Ok(Point { x: 0, y: 9 }), Point::from_str("0,9"));
+    assert_eq!(Ok(Point { x: 8, y: 0 }), Point::from_str("8,0"));
+    assert_eq!(Ok(Point { x: 9, y: 4 }), Point::from_str("9,4"));
+    assert_eq!(Ok(Point { x: 2, y: 2 }), Point::from_str("2,2"));
+}
+
+#[derive(Clone, Debug, PartialEq)]
+struct LineSegment {
+    start: Point,
+    end: Point,
+}
+
+impl FromStr for LineSegment {
+    type Err = Oopsie;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.split_once(" -> ") {
+            None => Err(Oopsie::InvalidSegment),
+            Some((startstr, endstr)) => {
+                let start = Point::from_str(startstr)?;
+                let end = Point::from_str(endstr)?;
+
+                Ok(LineSegment { start, end })
+            }
+        }
+    }
+}
+
+#[test]
+fn basic_segment_parsing() {
+    assert_eq!(
+        Ok(LineSegment {
+            start: Point { x: 0, y: 9 },
+            end: Point { x: 5, y: 9 }
+        }),
+        LineSegment::from_str("0,9 -> 5,9")
+    );
+    assert_eq!(
+        Ok(LineSegment {
+            start: Point { x: 8, y: 0 },
+            end: Point { x: 0, y: 8 }
+        }),
+        LineSegment::from_str("8,0 -> 0,8")
+    );
+}
+
+impl LineSegment {
+    fn max_x(&self) -> usize {
+        cmp::max(self.start.x, self.end.x)
+    }
+
+    fn max_y(&self) -> usize {
+        cmp::max(self.start.y, self.end.y)
+    }
+
+    fn is_horizontal(&self) -> bool {
+        self.start.y == self.end.y
+    }
+
+    fn is_vertical(&self) -> bool {
+        self.start.x == self.end.x
+    }
+
+    fn is_diagonal(&self) -> bool {
+        !self.is_horizontal() && !self.is_vertical()
+    }
+
+    fn slope(&self) -> (isize, isize) {
+        (
+            if self.start.x < self.end.x { 1 } else { -1 },
+            if self.start.y < self.end.y { 1 } else { -1 },
+        )
+    }
+}
+
+#[allow(dead_code)]
+struct Board {
+    data: Vec<u8>,
+    segments: Vec<LineSegment>,
+    width: usize,
+    height: usize,
+}
+
+impl Board {
+    fn new(width: usize, height: usize) -> Board {
+        Board {
+            data: vec![0; width * height],
+            segments: vec![],
+            width,
+            height,
+        }
+    }
+
+    fn get(&self, x: usize, y: usize) -> u8 {
+        self.data[(y * self.width) + x]
+    }
+
+    fn set(&mut self, x: usize, y: usize, value: u8) {
+        self.data[(y * self.width) + x] = value;
+    }
+
+    fn add_segment(&mut self, segment: LineSegment) {
+        if segment.is_vertical() {
+            let mut low = cmp::min(segment.start.y, segment.end.y);
+            let high = cmp::max(segment.start.y, segment.end.y);
+
+            while low <= high {
+                let current = self.get(segment.start.x, low);
+                self.set(segment.start.x, low, current + 1);
+                low += 1;
+            }
+        }
+
+        if segment.is_horizontal() {
+            let mut low = cmp::min(segment.start.x, segment.end.x);
+            let high = cmp::max(segment.start.x, segment.end.x);
+
+            while low <= high {
+                let current = self.get(low, segment.start.y);
+                self.set(low, segment.start.y, current + 1);
+                low += 1;
+            }
+        }
+
+        self.segments.push(segment);
+    }
+
+    fn add_diagonals(&mut self) {
+        let diagonals: Vec<LineSegment> = self
+            .segments
+            .iter()
+            .filter(|x| x.is_diagonal())
+            .cloned()
+            .collect();
+
+        for segment in diagonals.iter() {
+            if !segment.is_horizontal() && !segment.is_vertical() {
+                let (delta_x, delta_y) = segment.slope();
+                let mut x = segment.start.x as isize;
+                let mut y = segment.start.y as isize;
+                let target_x = segment.end.x as isize;
+                let target_y = segment.end.y as isize;
+
+                loop {
+                    let current = self.get(x as usize, y as usize);
+                    self.set(x as usize, y as usize, current + 1);
+
+                    if x == target_x && y == target_y {
+                        break;
+                    }
+
+                    x += delta_x;
+                    y += delta_y;
+                }
+            }
+        }
+    }
+
+    fn _print(&self) {
+        for y in 0..self.height {
+            for x in 0..self.width {
+                print!("{:02} ", self.get(x, y));
+            }
+            println!();
+        }
+    }
+
+    fn cross_overs(&self) -> usize {
+        self.data.iter().filter(|x| **x >= 2).count()
+    }
+}
+
+impl From<Vec<LineSegment>> for Board {
+    fn from(mut inputs: Vec<LineSegment>) -> Self {
+        let width = inputs.iter().map(|x| x.max_x()).max().unwrap();
+        let height = inputs.iter().map(|x| x.max_y()).max().unwrap();
+        let mut board = Board::new(width + 1, height + 1);
+
+        for segment in inputs.drain(..) {
+            board.add_segment(segment);
+        }
+
+        board
+    }
+}
+
+impl FromStr for Board {
+    type Err = Oopsie;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let segments = from_file_data(s)?;
+        Ok(Board::from(segments))
+    }
+}
+
+#[test]
+fn regression() {
+    let mut test_board = Board::from_str(TEST_DATA).unwrap();
+    assert_eq!(5, test_board.cross_overs());
+    test_board.add_diagonals();
+    assert_eq!(12, test_board.cross_overs());
+
+    let mut main_board = Board::from_str(DAY5_DATA).unwrap();
+    assert_eq!(7468, main_board.cross_overs());
+    main_board.add_diagonals();
+    assert_eq!(22364, main_board.cross_overs());
+}
+
+fn day5() -> Result<(), Oopsie> {
+    let mut main_board = Board::from_str(DAY5_DATA)?;
+
+    println!(
+        "Board has {} cross-overs without diagonals.",
+        main_board.cross_overs()
+    );
+    main_board.add_diagonals();
+    println!(
+        "Board has {} cross-overs with diagonals.",
+        main_board.cross_overs()
+    );
+
+    Ok(())
+}
+
+fn main() {
+    if let Err(e) = day5() {
+        println!("Top-level error: {}", e);
+    }
+}