2024 q8 urgh

Author: icecreamhead

twentytwentyfour/src/main/java/com/icecreamhead/adventofcode/q8/DiskFragmenter.java

@@ -0,0 +1,118 @@
+package com.icecreamhead.adventofcode.q8;
+
+import java.util.LinkedList;
+
+public class DiskFragmenter {
+
+  long pt1(String input) {
+    int[] blocks = generateBlocks(input);
+    compactBlocks(blocks);
+    return checksum(blocks);
+  }
+
+  long pt2(String input) {
+    int[] blocks = generateBlocks(input);
+    compactFiles(blocks);
+    return checksum(blocks);
+  }
+
+  static long checksum(int[] blocks) {
+    int i = 0;
+    long t = 0;
+    System.out.printf("length: %d\n", blocks.length);
+    while (i < blocks.length) {
+      if (blocks[i] != -1) {
+        t += blocks[i] * (long) i;
+      }
+      i++;
+    }
+    return t;
+  }
+
+  static void compactBlocks(int[] blocks) {
+    int l = 0, r = blocks.length - 1;
+    while (l < r) {
+      if (blocks[l] != -1) {
+        l++;
+      } else if (blocks[r] == -1) {
+        r--;
+      } else {
+        assert blocks[l] == -1 && blocks[r] != -1;
+        blocks[l] = blocks[r];
+        blocks[r] = -1;
+      }
+    }
+  }
+
+  static void compactFiles(int[] blocks) {
+//    System.out.printf("%s%n", new String(blocks));
+    int r = blocks.length - 1;
+    while (r >= 0) {
+
+      if (blocks[r] == -1) {
+        r--;
+      } else {
+        int rstart = r;
+        int val = blocks[r];
+        while (r >= 0 && blocks[r] == val) {
+          System.out.printf("block[%d] is %d\n", r, blocks[r]);
+          r--;
+        }
+        int rlen = rstart - r;
+
+                System.out.printf("len of %d is %d\n", val, rlen);
+
+        int emptySpace = findEmptySpaceOfSize(blocks, rlen, r);
+        System.out.println("empty space: " + emptySpace + " (started at " + 0 + ")");
+
+        if (emptySpace != -1) {
+          for (int i = 0; i < rlen; i++) {
+            blocks[emptySpace + i] = blocks[r + 1 + i];
+            blocks[r + 1 + i] = -1;
+          }
+        }
+//        System.out.printf("%s%n", new String(blocks));
+      }
+    }
+  }
+
+  private static int findEmptySpaceOfSize(int[] blocks, int reqlen, int max) {
+
+    for (int i = 0; i < max; i++) {
+
+      if (blocks[i] == -1) {
+        int blockstart = i;
+        while (i < max && blocks[i] != -1) {
+          System.out.printf("block[%d] is %d\n", i, blocks[i]);
+          i++;
+        }
+        int foundlen = 1 + i - blockstart;
+        System.out.printf("foundlen: %d\n", foundlen);
+        if (foundlen >= reqlen) return blockstart;
+      }
+
+    }
+    return -1;
+  }
+
+  static int[] generateBlocks(String input) {
+    boolean file = true;
+    int id = 0;
+
+    LinkedList<Integer> blocks = new LinkedList<>();
+    for (char c : input.toCharArray()) {
+      int repetitions = c - 48;
+
+      for (int i = 0; i < repetitions; i++) {
+        blocks.add(file ? id : -1);
+      }
+      if (file) {
+        id++;
+      }
+      file = !file;
+    }
+
+    return blocks.stream().mapToInt(i -> i).toArray();
+  }
+
+}