4 files changed, 285 insertions, 0 deletions

diff --git a/2020/day1/README.md b/2020/day1/README.md
new file mode 100644
index 0000000..f8ae070
--- /dev/null
+++ b/2020/day1/README.md
@@ -0,0 +1,13 @@
+# Day 1
+
+## First Part
+
+Simple two sum problem
+
+    perl sumto.pl
+
+## Second part
+
+[Three sum problem](https://www.callicoder.com/three-sum-problem/), which is like two sum problem after fixing the first index
+
+    perl threesum.pl
diff --git a/2020/day1/input b/2020/day1/input
new file mode 100644
index 0000000..b221b17
--- /dev/null
+++ b/2020/day1/input
@@ -0,0 +1,200 @@
+997
+1582
+1790
+1798
+1094
+1831
+1879
+1730
+1995
+1702
+1680
+1869
+1964
+1777
+1862
+1928
+1997
+1741
+1604
+1691
+1219
+1458
+1749
+1717
+1786
+1665
+1724
+1998
+1589
+1828
+1953
+1848
+1500
+1590
+1968
+1948
+1323
+1800
+1986
+679
+1907
+1916
+1820
+1661
+1479
+1808
+1824
+1825
+1952
+1666
+1541
+1791
+1906
+1638
+1557
+1999
+1710
+1549
+1912
+1974
+1628
+1748
+1411
+1978
+1865
+1932
+1839
+1892
+1981
+1807
+357
+912
+1443
+1972
+1816
+1890
+1029
+1175
+1522
+1750
+2001
+1655
+1955
+1949
+1660
+233
+1891
+1994
+1934
+1908
+1573
+1712
+1622
+1770
+1574
+1778
+1851
+2004
+1818
+1200
+1229
+1110
+1005
+1716
+1765
+1835
+1773
+15
+1914
+1833
+1689
+1843
+1718
+1872
+390
+1941
+1178
+1670
+1899
+1864
+1913
+2010
+1855
+1797
+1767
+1673
+1657
+1607
+1305
+1341
+1662
+1845
+1980
+1534
+1789
+1876
+1849
+1926
+1958
+977
+1709
+1647
+1832
+1785
+1854
+1667
+1679
+1970
+1186
+2000
+1681
+1684
+1614
+1988
+1561
+1594
+1636
+1327
+1696
+1915
+1045
+1829
+1079
+1295
+1213
+1714
+1992
+1984
+1951
+1687
+1842
+1792
+87
+1732
+428
+1799
+1850
+1962
+1629
+1965
+1142
+1040
+131
+1844
+1454
+1779
+1369
+1960
+1887
+1725
+1893
+1465
+1676
+1826
+1462
+1408
+1937
+1643
+1069
+1759
diff --git a/2020/day1/sumto.pl b/2020/day1/sumto.pl
new file mode 100644
index 0000000..931f5e2
--- /dev/null
+++ b/2020/day1/sumto.pl
@@ -0,0 +1,28 @@
+use strict;
+use warnings;
+use DDP;
+use Smart::Comments;
+
+open my $fh, '<', "input" or die "no input present, $!";
+chomp(my @nums = <$fh>);
+close $fh;
+
+@nums = sort { $a <=> $b } @nums;
+
+my $l_idx = 0;
+my $r_idx = $#nums;
+
+my $total = $nums[$l_idx] + $nums[$r_idx];
+
+while ($total != 2020) {
+
+    if ($total < 2020) {
+        $l_idx++; # total too low, increase
+    } else {
+        $r_idx--; # total too high, decrease
+    }
+
+    $total = $nums[$l_idx] + $nums[$r_idx];
+}
+
+print $nums[$l_idx] * $nums[$r_idx];
diff --git a/2020/day1/threesum.pl b/2020/day1/threesum.pl
new file mode 100644
index 0000000..8f2083a
--- /dev/null
+++ b/2020/day1/threesum.pl
@@ -0,0 +1,44 @@
+use strict;
+use warnings;
+use DDP;
+# use Smart::Comments;
+
+open my $fh, '<', "input" or die "no input present, $!";
+chomp(my @nums = <$fh>);
+close $fh;
+
+@nums = sort { $a <=> $b } @nums;
+
+# fix one index, solve two sum problem
+my $fixed_idx = 0;
+my $l_idx = 1;
+my $r_idx = $#nums;
+
+my $total = $nums[$fixed_idx] + $nums[$l_idx] + $nums[$r_idx];
+
+while ($total != 2020) {
+
+    if ($total < 2020) {
+        $l_idx++; # total too low, increase
+    } else {
+        $r_idx--; # total too high, decrease
+    }
+
+    # fixed index might not be correct
+    if ($l_idx > $r_idx) {
+        $fixed_idx++;
+        $l_idx = $fixed_idx + 1;
+        $r_idx = $#nums;
+    }
+
+    $total = $nums[$fixed_idx] + $nums[$l_idx] + $nums[$r_idx];
+    ### $total
+
+    ### $fixed_idx
+    ### $l_idx
+    ### $r_idx
+
+    # print("fixed: $nums[$fixed_idx]\nleft: $nums[$l_idx]\nright: $nums[$r_idx]\n");
+}
+
+print $nums[$fixed_idx] * $nums[$l_idx] * $nums[$r_idx];