p1726

Author: ian-hon

src/main.rs

@@ -1,5 +1,5 @@
-mod p1790;
+mod p1726;
 
 pub fn main() {
-    p1790::run();
+    p1726::run();
 }

src/p1726.rs

@@ -0,0 +1,46 @@
+use std::collections::HashMap;
+
+pub fn run() {
+    for i in [
+        vec![2,3,4,6],
+        vec![1,2,4,5,10]
+    ] {
+        println!("{}", tuple_same_product(i));
+    }
+}
+
+pub fn tuple_same_product(nums: Vec<i32>) -> i32 {
+    let mut pairs: HashMap<i32, i32> = HashMap::new();
+
+    for n in 0..nums.len() {
+        for i in &nums[(n + 1)..nums.len()] {
+            let p = nums[n] * *i;
+            match pairs.get_mut(&p) {
+                Some(m) => {
+                    *m += 1;
+                },
+                None => {
+                    pairs.insert(p, 1);
+                }
+            }
+        }
+    }
+
+    let mut count = 0;
+
+    for (_, v) in pairs {
+        if v <= 1 {
+            continue;
+        }
+
+        count += 8 * compounded_sum(v);
+    }
+
+    count
+}
+
+pub fn compounded_sum(i: i32) -> i32 {
+    // area of triangle
+    let i = i - 1;
+    ((i * i) + i) / 2
+}