add abc417c.rs

rchaser53 · rchaser53 · commit b4b67b53d1d0 · 2025-08-11T17:44:01.000+09:00
diff --git a/src/abc/abc417c.rs b/src/abc/abc417c.rs
@@ -0,0 +1,31 @@
+/** THIS IS AN OUTPUT FILE. NOT EDIT THIS FILE DIRECTLY. **/
+use proconio::input;
+use proconio::marker::*;
+use std::marker::PhantomData;
+use std::cmp::*;
+use std::collections::*;
+
+fn main() {
+  input! {
+    n:usize,
+    a:[isize;n]
+  }
+
+  let mut map1 = HashMap::new();
+  let mut map2 = HashMap::new();
+  for i in 0..n {
+    let ai = i as isize + 1;
+
+    *map1.entry((ai-a[i])).or_insert(0) += 1;
+    *map2.entry((ai+a[i])).or_insert(0) += 1;
+  }
+
+  let mut result = 0usize;
+  for (x, num) in map1.iter() {
+    if let Some(&num2) = map2.get(x) {
+      result += num * num2;
+    }
+  }
+
+  println!("{}", result);
+}
