046 ok

046/main.rs

@@ -0,0 +1,59 @@
+use std::collections::HashSet;
+
+type HS = HashSet<u32>;
+
+fn er() -> HS {
+    let mut nums = Vec::new();
+    let size = 1_000_000;
+    for n in 0..size+1 { nums.push(true); }
+    let mut p = 1;
+    loop {
+        let mut found = false;
+        for i in p+1..size {
+            if nums[i] {
+                found = true;
+                p = i;
+                break;
+            }
+        }
+        if !found { break; }
+        for i in (2 * p .. size).step_by(p) {
+            nums[i] = false;
+        }
+    }
+    let mut res = HashSet::new();
+    for i in 2..size {
+        if nums[i] { res.insert(i as u32); }
+    }
+    return res;
+}
+
+fn sqs() -> HS {
+    let mut res = HS::new();
+    for n in 1..1_000_0 {
+        res.insert(n*n);
+    }
+    return res;
+}
+
+fn test(n: u32, ps: &HS, sq: &HS) -> bool {
+    for k in 7..n {
+        if !ps.contains(&k) { continue }
+        let s = (n - k) / 2;
+        if !sq.contains(&s) { continue }
+        return true;
+    }
+    return false;
+}
+
+fn main() {
+    let ps = er();
+    let sq = sqs();
+    for k in (9..100000).step_by(2) {
+        if ps.contains(&k) { continue; }
+        if !test(k, &ps, &sq) {
+            println!("{}", k);
+            break;
+        }
+    }
+}