day 5

day05/sample

@@ -0,0 +1,11 @@
+3-5
+10-14
+16-20
+12-18
+
+1
+5
+8
+11
+17
+32

day05/sol.py

@@ -0,0 +1,57 @@
+def parse(input):
+    ranges = []
+    ids = []
+    with open(input) as f:
+        for line in f:
+            line = line.strip()
+            if line == "":
+                break
+            lo, _, hi = line.partition("-")
+            ranges.append((int(lo), int(hi)))
+        for line in f:
+            ids.append(int(line.strip()))
+    return ranges, ids
+
+def solve(input):
+    # Part 1: count the number of given ids which are within one of the ranges
+    ranges, ids = parse(input)
+    t = 0
+    for x in ids:
+        for lo,hi in ranges:
+            if lo <= x <= hi:
+                t += 1
+                break
+    print(t)
+
+
+    # Part 2: count the number of possible ids which are within one of the ranges --
+    # in other words, the size of the union of all the ranges.
+    #
+    # We start by flattening the ranges so that they don't overlap with each other
+    flattened = []
+    queue = list(ranges)
+    while queue:
+        lo, hi = queue.pop()
+        found = False
+        for i,(x,y) in enumerate(flattened):
+            if not (hi < x or y < lo):
+                found = True
+                break
+        if found:
+            #print("collapsing ({:,} {:,}) and ({:,} {:,}) -> ({:,} {:,})".format(x,y,lo,hi,min(x,lo),max(y,hi)))
+            # if x <= lo <= hi < y then the range is unchanged and we don't need to update flattened[i].
+            # otherwise we need to add the new range to the queue to see if it can be merged with any other entries.
+            if lo < x or hi > y:
+                del flattened[i]
+                queue.append((min(x,lo), max(y,hi)))
+        else:
+            flattened.append((lo,hi))
+
+    # Then we sum up their sizes. Ranges are inclusive, so +1.
+    t = 0
+    for x,y in flattened:
+        t += y-x + 1
+    print(t)
+
+solve("sample")
+solve("input")