Add solutions for day 3.

2016/day-03/sample.txt

@@ -0,0 +1,6 @@
+101 301 501
+102 302 502
+103 303 503
+201 401 601
+202 402 602
+203 403 603

2016/day-03/solution.rs

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+use std::env;
+use std::io::prelude::*;
+use std::io::BufReader;
+use std::fs::File;
+
+fn is_triangle(mut triangle: Vec<i32>) -> bool
+{
+    triangle.sort();
+
+    return triangle[0] + triangle[1] > triangle[2];
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    let f = File::open(&args[1]).expect("Could not open file");
+    let reader = BufReader::new(f);
+
+    let mut horizontal = 0;
+    let mut all_nums: Vec<i32> = Vec::new();
+
+    for line in reader.lines() {
+        let numbers: Vec<i32> = line.unwrap()
+            .split(' ')
+            .map(|s| s.trim())
+            .filter(|s| !s.is_empty())
+            .map(|s| s.parse().unwrap())
+            .collect();
+
+        for num in &numbers {
+            all_nums.push(*num);
+        }
+
+        if is_triangle(numbers) {
+            horizontal += 1;
+        }
+
+    }
+
+    let mut vertical = 0;
+
+    for i in 0..(all_nums.len() / 9) {
+        let offset = i * 9;
+        for j in 0..3 {
+            let triangle = vec![all_nums[offset + j + 0], all_nums[offset + j + 3], all_nums[offset + j + 6]];
+
+            if is_triangle(triangle) {
+                vertical += 1;
+            }
+        }
+    }
+
+    println!("{} triangles possible horizontally", horizontal);
+    println!("{} triangles possible vertically", vertical);
+}