complete 2042.rs 2357.rs 6549.rs 10090.rs

storage/zeta/rs/completed/10090.rs

@@ -0,0 +1,62 @@
+use std::io::{read_to_string, stdin};
+
+fn invcnt(arr: &mut Vec<usize>, lo: usize, hi: usize) -> usize {
+    let delta = hi - lo;
+    if delta == 0 {
+        return 0;
+    } else if delta == 1 {
+        return 0;
+    } else if delta == 2 {
+        if arr[lo] > arr[lo + 1] {
+            let temp = arr[lo + 1];
+            arr[lo + 1] = arr[lo];
+            arr[lo] = temp;
+            return 1;
+        } else {
+            return 0;
+        }
+    } else {
+        let mut res = 0;
+        let mut left = lo;
+        let mut right = (lo + hi) / 2;
+        let left_end = right;
+        let right_end = hi;
+        let mut v = vec![];
+        res += invcnt(arr, left, left_end);
+        res += invcnt(arr, right, right_end);
+        while left < left_end && right < right_end {
+            if arr[left] > arr[right] {
+                v.push(arr[right]);
+                res += left_end - left;
+                right += 1;
+            } else {
+                v.push(arr[left]);
+                left += 1;
+            }
+        }
+        while left < left_end {
+            v.push(arr[left]);
+            left += 1;
+        }
+        while right < right_end {
+            v.push(arr[right]);
+            right += 1;
+        }
+        for (i, &e) in v.iter().enumerate() {
+            arr[lo + i] = e;
+        }
+        return res;
+    }
+}
+
+fn main() {
+    let temp = read_to_string(stdin()).unwrap();
+    let mut iter = temp
+        .split_ascii_whitespace()
+        .map(|x| x.parse::<usize>().unwrap());
+    let n = iter.next().unwrap();
+    let mut arr = (0..n).map(|_| iter.next().unwrap()).collect::<Vec<_>>();
+
+    let res = invcnt(&mut arr, 0, n);
+    println!("{}", res);
+}