zipping iterators is slower but uses less memory.

find_pivot_index/src/main.rs

@@ -1,5 +1,5 @@
 fn main() {
-    println!("Hello, world!");
+    dbg!(f(vec![2, 1, -1]));
 }
 
 fn f(nums: Vec<i32>) -> i32 {
@@ -9,12 +9,11 @@ fn f(nums: Vec<i32>) -> i32 {
         cur += n;
         rights.push(cur);
     }
-    rights.reverse();
     let rights = &rights;
     cur = 0;
-    for (i, num) in nums.into_iter().enumerate() {
-        cur += num;
-        if cur == rights[i] {
+    for (i, (left, &right)) in nums.iter().zip(rights.iter().rev()).enumerate() {
+        cur += left;
+        if cur == right {
             return i as i32;
         }
     }