add write_and_erase.rs

src/write_and_erase.rs

@@ -0,0 +1,23 @@
+#![allow(unused_imports)]
+use proconio::input;
+use proconio::marker::*;
+use std::collections::HashMap;
+
+fn main() {
+  input!{
+    n: usize,
+    vals: [usize;n] 
+  }
+
+  let mut map = HashMap::new();
+  for v in vals {
+    let entry = map.entry(v).or_insert(false);
+    *entry = !(*entry);
+  }
+
+  let mut count = 0;
+  for (_, v) in map {
+    if v { count += 1; }
+  }
+  println!("{}", count);
+}