merge_intervals gives wrong results

Done

/home/devdi/devswarm/evals/tasks/merge_intervals/repo · 2026-11-09 16:18:28 UTC · took 25.2s

Plan (done)
Code (done)
Test (done)
Review (done)
Finish (done)

Cost

$0.0028

Tests

Passed

Iterations

Re-plans

LLM calls

Prompt read from cache

80%

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Cost per agent

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Output

View as table

Agent	Cost	Cache read	Cache write	Input	Output
planner	$0.0008	5,810	948	8	1,305
coder	$0.0009	9,170	2,334	8	1,037
tester	$0.0011	10,941	3,268	8	1,158

Timeline

planner iteration 1 Finished 3 calls · 8,071 tokens · $0.0008 · 9.5s

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coder iteration 1 Finished 3 calls · 12.5K tokens · $0.0009 · 6.7s

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tester iteration 1 Finished 3 calls · 15.4K tokens · $0.0011 · 7.8s

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verify iteration 1 Passed 0.5s

............                                                             [100%]
12 passed in 0.02s

Final diff

diff --git a/intervals.py b/intervals.py
index 76e6d7f..2bafff4 100644
--- a/intervals.py
+++ b/intervals.py
@@ -1,8 +1,8 @@
 def merge_intervals(intervals: list[tuple[int, int]]) -> list[tuple[int, int]]:
     merged: list[tuple[int, int]] = []
-    for start, end in intervals:
-        if merged and start < merged[-1][1]:
-            merged[-1] = (merged[-1][0], end)
+    for start, end in sorted(intervals):
+        if merged and start <= merged[-1][1]:
+            merged[-1] = (merged[-1][0], max(merged[-1][1], end))
         else:
             merged.append((start, end))
     return merged
diff --git a/test_intervals.py b/test_intervals.py
index 1e6a250..c3edf81 100644
--- a/test_intervals.py
+++ b/test_intervals.py
@@ -7,3 +7,49 @@ def test_overlap():
 
 def test_separate():
     assert merge_intervals([(1, 2), (3, 4)]) == [(1, 2), (3, 4)]
+
+
+def test_touching_merge():
+    assert merge_intervals([(1, 2), (2, 3)]) == [(1, 3)]
+
+
+def test_unsorted_input():
+    assert merge_intervals([(5, 6), (1, 2)]) == [(1, 2), (5, 6)]
+
+
+def test_contained_does_not_shrink():
+    assert merge_intervals([(1, 10), (2, 3)]) == [(1, 10)]
+
+
+def test_empty():
+    assert merge_intervals([]) == []
+
+
+def test_input_not_mutated():
+    data = [(5, 6), (1, 2)]
+    merge_intervals(data)
+    assert data == [(5, 6), (1, 2)]
+
+
+def test_single_interval():
+    assert merge_intervals([(1, 2)]) == [(1, 2)]
+
+
+def test_unsorted_chain_merges():
+    assert merge_intervals([(4, 6), (1, 3), (2, 5)]) == [(1, 6)]
+
+
+def test_unsorted_contained_listed_first():
+    assert merge_intervals([(2, 3), (1, 10)]) == [(1, 10)]
+
+
+def test_equal_starts():
+    assert merge_intervals([(1, 5), (1, 2)]) == [(1, 5)]
+    assert merge_intervals([(1, 2), (1, 5)]) == [(1, 5)]
+
+
+def test_unsorted_input_not_mutated_order_preserved():
+    data = [(3, 4), (1, 2), (2, 3)]
+    original = list(data)
+    assert merge_intervals(data) == [(1, 4)]
+    assert data == original