c1: first working impl

src/main.rs

@@ -1,3 +1,58 @@
-fn main() {
-    println!("Hello, world!");
+use std::io;
+
+fn triangle_area(x1: f64, y1: f64, x2: f64, y2: f64, x3: f64, y3: f64) -> f64 {
+    ((x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)) / 2.0).abs()
+}
+
+// We use the barycentric coordinate method to decide whether
+// given point lies within the triangle. It took me more than
+// I would like to admit to remember that name.
+fn main() {
+    let mut input = String::new();
+
+    println!("Enter the coordinates for the triangle's vertices (x1 y1 x2 y2 x3 y3):");
+    io::stdin().read_line(&mut input).unwrap();
+    let coords: Vec<f64> = input
+        .trim()
+        .split_whitespace()
+        .filter_map(|x| x.parse::<f64>().ok())
+        .collect();
+
+    if coords.len() != 6 {
+        println!("Invalid input: expected 6 numbers for the triangle's vertices.");
+        return;
+    }
+
+    let (x1, y1, x2, y2, x3, y3) = (
+        coords[0], coords[1], coords[2], coords[3], coords[4], coords[5],
+    );
+
+    input.clear();
+    println!("Enter the coordinates for the point to test (px py):");
+    io::stdin().read_line(&mut input).unwrap(); // I'm getting executed for this unwrap
+    let point: Vec<f64> = input
+        .trim()
+        .split_whitespace()
+        .filter_map(|x| x.parse::<f64>().ok())
+        .collect();
+
+    if point.len() != 2 {
+        println!("Invalid input: expected 2 numbers for the point's coordinates.");
+        return;
+    }
+
+    let (px, py) = (point[0], point[1]);
+
+    // calculate areas
+    let total_area = triangle_area(x1, y1, x2, y2, x3, y3);
+    let area1 = triangle_area(px, py, x2, y2, x3, y3);
+    let area2 = triangle_area(x1, y1, px, py, x3, y3);
+    let area3 = triangle_area(x1, y1, x2, y2, px, py);
+
+    // check if the sum of the smaller areas matches the total area
+    if (area1 + area2 + area3 - total_area).abs() < 1e-9 {
+        println!("The point ({}, {}) lies inside the triangle.", px, py);
+    } else {
+        println!("The point ({}, {}) lies outside the triangle.", px, py);
+    }
 }