d09

day09/d09p2.swift

@@ -0,0 +1,56 @@
+import Foundation
+
+func readInput(_ filePath: String) throws -> Disk {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+        .trimmingCharacters(in: .whitespacesAndNewlines)
+        .map { Int(String([$0]))! }
+    var pos = 0
+    var data: [(Int, Int)] = []
+    var free: [(Int, Int)] = []
+    for (i, x) in content.enumerated() {
+        if i.isMultiple(of: 2) {
+            data.append((pos, x))
+        } else {
+            free.append((pos, x))
+        }
+        pos += x
+    }
+    return Disk(data: data, free: free)
+}
+
+func sumRange(start: Int, len: Int) -> Int {
+    return len * (start + start + len - 1) / 2
+}
+
+struct Disk {
+    var data: [(Int, Int)]
+    var free: [(Int, Int)]
+    var csum: Int = 0
+
+    mutating func compact() {
+        for fileNo in (0..<data.count).reversed() {
+            var moved = false
+            let (iData, dataBlock) = data[fileNo]
+            for freeNo in 0..<free.count {
+                let (iFree, freeBlock) = free[freeNo]
+                if iFree > iData {
+                    break
+                }
+                if freeBlock >= dataBlock {
+                    csum += fileNo * sumRange(start: iFree, len: dataBlock)
+                    free[freeNo] = (iFree + dataBlock, freeBlock - dataBlock)
+                    data[fileNo] = (iData, 0)
+                    moved = true
+                    break
+                }
+            }
+            if !moved {
+                csum += fileNo * sumRange(start: iData, len:dataBlock)
+            }
+        }
+    }
+}
+
+var disk = try readInput(CommandLine.arguments[1])
+disk.compact()
+print(disk.csum)