Largest number

Author: volodimyr

179.largest_number/numbers.py

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+# 179. Largest number
+# Topics: 'Array', 'String', 'Greedy', 'Sorting'
+# Level: 'Medium'
+
+# Given a list of non-negative integers nums, arrange them such that they form the largest number and return it.
+
+# Since the result may be very large, so you need to return a string instead of an integer.
+
+ 
+
+# Example 1:
+
+# Input: nums = [10,2]
+# Output: "210"
+
+# Example 2:
+
+# Input: nums = [3,30,34,5,9]
+# Output: "9534330"
+
+ 
+
+# Constraints:
+
+#     1 <= nums.length <= 100
+#     0 <= nums[i] <= 109
+
+from functools import cmp_to_key
+from typing import List
+
+class Solution:
+    def largestNumber(self, nums: List[int]) -> str:
+        nums_str = list(map(str, nums))
+        def compare(x, y):
+            if x + y > y + x:
+                return -1
+            elif x + y < y + x:
+                return 1
+            return 0
+        nums_str.sort(key=cmp_to_key(compare))
+        if nums_str[0] == '0':
+            return nums_str[0]
+        return ''.join(nums_str)

179.largest_number/test_numbers.py

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+import unittest
+from numbers import Solution   # adjust if your file name differs
+
+class TestLargestNumber(unittest.TestCase):
+
+    def test_example_1(self):
+        self.assertEqual(Solution().largestNumber([10, 2]), "210")
+
+    def test_example_2(self):
+        self.assertEqual(Solution().largestNumber([3, 30, 34, 5, 9]), "9534330")
+
+    def test_single_element(self):
+        self.assertEqual(Solution().largestNumber([1]), "1")
+
+    def test_zero(self):
+        self.assertEqual(Solution().largestNumber([0]), "0")
+
+    def test_all_zeros(self):
+        self.assertEqual(Solution().largestNumber([0, 0]), "0")
+
+    def test_prefix_case(self):
+        # tricky: 121 vs 12
+        self.assertEqual(Solution().largestNumber([121, 12]), "12121")
+
+    def test_duplicates(self):
+        self.assertEqual(
+            Solution().largestNumber([8308, 8308, 830]),
+            "83088308830"
+        )
+
+    def test_large_numbers(self):
+        self.assertEqual(
+            Solution().largestNumber([999999998, 999999997]),
+            "999999998999999997"
+        )
+
+    def test_compare_edge_conflict(self):
+        # 343 + 34 = 34334
+        # 34 + 343 = 34343 → larger
+        self.assertEqual(
+            Solution().largestNumber([343, 34]),
+            "34343"
+        )
+
+    def test_many_zeros_with_nonzero(self):
+        self.assertEqual(
+            Solution().largestNumber([0, 0, 1, 0]),
+            "1000"
+        )
+
+    def test_max_input_size(self):
+        nums = [10**9] * 100
+        expected = "1000000000" * 100
+        self.assertEqual(Solution().largestNumber(nums), expected)
+
+
+if __name__ == "__main__":
+    unittest.main()