var -> let

Co-authored-by: yhkee0404 <[email protected]>

Author: sonjh1217

pacific-atlantic-water-flow/sonjh1217.swift

@@ -20,7 +20,7 @@ class Solution {
             }
 
             while head < queue.count {
-                var (i, j) = queue[head]
+                let (i, j) = queue[head]
                 head += 1
 
                 for (di, dj) in directions {