added day01

Signed-off-by: Philip Molares <philip.molares@udo.edu>

day01/Cargo.lock

+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day01"
+version = "0.1.0"

day01/Cargo.toml

+[package]
+name = "day01"
+version = "0.1.0"
+authors = ["Philip Molares <philip.molares@udo.edu>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day01/input.txt

+1509
+1857
+1736
+1815
+1576
+1970
+1567
+1778
+1508
+1833
+1377
+1890
+1375
+1396
+1102
+1639
+1818
+1469
+1138
+1333
+1906
+1557
+1686
+1712
+1990
+1930
+1761
+1881
+1551
+1627
+1801
+1728
+1960
+1407
+1832
+1842
+1393
+1870
+1295
+1528
+251
+1945
+1589
+1850
+1650
+1793
+1997
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+1697
+1081
+1825
+1899
+1171
+1104
+1839
+1974
+1630
+1831
+1671
+1723
+1811
+1489
+1647
+1486
+1107
+1786
+1680
+1942
+1640
+1112
+1703
+1315
+1769
+1966
+997
+2010
+1635
+1196
+383
+1986
+1860
+1743
+1756
+1555
+1111
+1823
+48
+1953
+1083
+1804
+1933
+1626
+1895
+1807
+1669
+1783
+389
+1821
+1883
+1114
+1587
+1941
+1725
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+456
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+1939
+1975
+1324
+1201
+1018
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+1402
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+1481
+1633
+1781
+1622
+1822
+1559
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+1510
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+1813
+1695
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+704
+1964
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+1763
+1656
+1183
+1771
+1276
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+1810
+1992
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+1318
+1965
+1943
+1549
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+1506
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+1787
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+1817
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+1982
+1667
+1753
+1041
+1826
+1961
+1797
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+1720
+1835
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+1977
+1971
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+1661
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+1162
+1755
+1846
+1674
+1698
+1882
+1766
+1820
+1531
+1577
+1710
+1382
+1246
+1864
+1702

day01/src/main.rs

+use std::fs::File;
+use std::io::{self, prelude::*, BufReader};
+
+const WANTED_SUM: i64 = 2020;
+
+fn find_sum(numbers: &[i64], first: &mut usize, last: &mut usize, wanted_sum: i64) {
+    while first < last {
+        let sum = numbers[*first] + numbers[*last];
+        if sum < wanted_sum {
+            *first += 1;
+        } else if sum > wanted_sum {
+            *last -= 1;
+        } else {
+            break;
+        }
+    }
+}
+
+fn main() -> io::Result<()> {
+    println!("Advent of Code 2020 – Day 1:");
+
+    let file = File::open("input.txt")?;
+    let reader = BufReader::new(file);
+
+    let mut input_numbers: Vec<i64> = reader
+        .lines()
+        .map(|l| {
+            l.unwrap()
+                .parse::<i64>()
+                .expect("Error: Could not parse each line")
+        })
+        .collect();
+
+    input_numbers.sort();
+
+    let mut first = 0;
+    let mut last = input_numbers.len() - 1; 
+
+    find_sum(&input_numbers, &mut first, &mut last, WANTED_SUM);
+
+    let product: i64 = input_numbers[first] * input_numbers[last];
+
+    println!("Answer Part 1: {} * {} = {}", input_numbers[first], input_numbers[last], product);
+
+    let mut middle = 0;
+
+    for index in 0..(input_numbers.len() - 1) {
+        first = index + 1;
+        last = input_numbers.len() - 1;
+        find_sum(&input_numbers, &mut first, &mut last, WANTED_SUM-input_numbers[index]);
+        let sum = input_numbers[first] + input_numbers[index] + input_numbers[last];
+        if sum == WANTED_SUM {
+            middle = index;
+            break;
+        }
+    }
+
+    let product2: i64 = input_numbers[first] * input_numbers[middle] * input_numbers[last];
+
+    println!("Answer Part 2: {} * {} * {} = {}", input_numbers[first], input_numbers[middle], input_numbers[last], product2);
+
+    Ok(())
+}