Day 09

day09.groovy

@@ -0,0 +1,66 @@
+import groovy.transform.TupleConstructor;
+import groovy.transform.ToString;
+
+
+List sequenceDiff(List seq) {
+    def result = [];
+    for (int i = 0; i < seq.size() - 1; i++) {
+        result << (seq[i + 1] - seq[i]);
+    }
+    return result;
+}
+
+{ // Test: sequenceDiff
+    def d1 = sequenceDiff([0, 3, 6, 9, 12, 15]);
+    assert d1.size() == 5;
+    assert d1[0] == 3;
+    assert d1[-1] == 3;
+
+    def d2 = sequenceDiff([1, 3, 6, 10, 15, 21]);
+    assert d2.size() == 5;
+    assert d2[0] == 2;
+    assert d2[-1] == 6;
+}
+
+boolean sequenceIsAllZeros(List seq) {
+    for (int i = 0; i < seq.size(); i++) {
+        if (seq[i] != 0) {
+            return false;
+        }
+    }
+    return true;
+}
+
+{ // Test: sequence is all zeros
+    assert sequenceIsAllZeros([1, 0, 0]) == false;
+    assert sequenceIsAllZeros([0, 1, 0]) == false;
+    assert sequenceIsAllZeros([0, 0, 1]) == false;
+    assert sequenceIsAllZeros([0, 0, 0]) == true;
+}
+
+def extendSequence(List seqs) {
+    // forwards
+    for (int i = seqs.size() - 1; i >= 0; i--) {
+        seqs[i - 1] << (seqs[i - 1][-1] + seqs[i][-1]);
+    }
+    // backwards
+    for (int i = seqs.size() - 1; i >= 0; i--) {
+        seqs[i - 1].add(0, seqs[i - 1][0] - seqs[i][0]);
+    }
+}
+
+def inputs = new File("input/day09.txt").readLines().collect { it.split(/\s+/).collect { it.toLong() } };
+
+inputs.collect { input -> 
+    def seqs = [input];
+    while(!sequenceIsAllZeros(seqs[-1])) {
+        seqs << sequenceDiff(seqs[-1]);
+    }
+    return seqs;
+}.each { 
+    extendSequence(it);
+}.collect {
+    [it[0][0], it[0][-1]]
+}.inject([0, 0]) { acc, it -> 
+    [acc[0] + it[0], acc[1] + it[1]] 
+}.each { println(it) };