bugget 003, but ok

003/solution.rs

@@ -0,0 +1,45 @@
+// sqrt(600_851_475_143) = 775146.09922 ~= 775147
+
+fn get_sqrt_ceil(x: u64) -> u64 {
+    let xf: f64 = x as f64;
+    let sq: f64 = xf.sqrt().ceil();
+    let res: u64 = sq as u64;
+    return res;
+}
+
+fn get_biggest_div(n: u64) -> u64 {
+    // println!("get_biggest_div from {}", n);
+    let mut d: u64 = 1u64;
+    let sq = get_sqrt_ceil(n);
+    for k in 2u64..=sq {
+        if n % k == 0 { d = k; }
+    }
+    if d == 1 { return n; }
+    let dd = get_biggest_div(n / d);
+    if dd > d {
+        return dd;
+    } else {
+        return d;
+    }
+}
+
+fn find_biggest_prime_div(n: u64) -> u64 {
+    let biggest_div = get_biggest_div(n);
+    if biggest_div == n {
+        return n;
+    }
+    let p = find_biggest_prime_div(biggest_div);
+    let q = find_biggest_prime_div(n / biggest_div);
+    if p > q {
+        return p;
+    } else {
+        return q;
+    }
+}
+
+
+fn main() {
+    //let r = find_biggest_prime_div(600_851_475_143);
+    let r = find_biggest_prime_div(600_851_475_143);
+    println!("{}", r);
+}