AlgoExpert Three Number Sum

Author: raul-sauco

README.md

@@ -1091,6 +1091,7 @@ First column links to the problem in AlgoExpert, second is the problem's difficu
 | [Selection Sort][ae&selection-sort]                                         | 🟢 Easy      | [![python](res/py.png)][ae&selection-sort#py]                     |
 | [Sorted Squared Array][ae&sorted-squared-array]                             | 🟢 Easy      | [![python](res/py.png)][ae&sorted-squared-array#py]               |
 | [Spiral Traverse][ae&spiral-traverse]                                       | 🟠 Medium    | [![python](res/py.png)][ae&spiral-traverse#py]                    |
+| [Three Number Sum][ae&three-number-sum]                                     | 🟠 Medium    | [![python](res/py.png)][ae&three-number-sum#py]                   |
 | [Two Number Sum][ae&two-number-sum]                                         | 🟢 Easy      | [![python](res/py.png)][ae&two-number-sum#py]                     |
 | [Validate BST][ae&validate-bst]                                             | 🟠 Medium    | [![python](res/py.png)][ae&validate-bst#py]                       |
 | [Validate Subsequence][ae&validate-subsequence]                             | 🟢 Easy      | [![python](res/py.png)][ae&validate-subsequence#py]               |
@@ -1146,6 +1147,8 @@ First column links to the problem in AlgoExpert, second is the problem's difficu
 [ae&sorted-squared-array#py]: algoexpert/sorted-squared-array.py
 [ae&spiral-traverse]: https://www.algoexpert.io/questions/spiral-traverse
 [ae&spiral-traverse#py]: algoexpert/spiral-traverse.py
+[ae&three-number-sum]: https://www.algoexpert.io/questions/three-number-sum
+[ae&three-number-sum#py]: algoexpert/three-number-sum.py
 [ae&two-number-sum]: https://www.algoexpert.io/questions/two-number-sum
 [ae&two-number-sum#py]: algoexpert/two-number-sum.py
 [ae&validate-bst]: https://www.algoexpert.io/questions/validate-bst

algoexpert/three-number-sum.py

@@ -0,0 +1,66 @@
+# Three Number Sum
+# 🟠 Medium
+#
+# https://www.algoexpert.io/questions/three-number-sum
+#
+# Tags: Array, Two Pointer, Sorting
+
+import timeit
+
+
+# Find all combinations of three numbers in the input that add up to the
+# target sum by fixing one number at a time and using two pointers to
+# find combinations of other two numbers that make up to the sum.
+#
+# Time complexity: O(n^2) - For each value in the array, we explore all
+# combinations of other two values in linear time.
+# Space complexity: O(1) - If we don't count the output or input arrays.
+class Solution:
+    def threeNumberSum(self, array, targetSum):
+        array.sort()
+        res = []
+        # Fix the leftmost element, then use two pointers to find all
+        # combinations of other two values that add to the target sum.
+        for i in range(len(array) - 2):
+            l, r = i + 1, len(array) - 1
+            while l < r:
+                val = array[i] + array[l] + array[r]
+                if val == targetSum:
+                    res.append((array[i], array[l], array[r]))
+                    l += 1
+                    r -= 1
+                elif val < targetSum:
+                    l += 1
+                else:
+                    r -= 1
+        return res
+
+
+def test():
+    executors = [
+        Solution,
+    ]
+    tests = [
+        [[8, 10, -2, 49, 14], 57, [(-2, 10, 49)]],
+        [[1, 2, 3, 4, 5, 6, 7, 8, 9, 15], 29, [(5, 9, 15), (6, 8, 15)]],
+        [[12, 3, 1, 2, -6, 5, -8, 6], 0, [(-8, 2, 6), (-8, 3, 5), (-6, 1, 5)]],
+    ]
+    for executor in executors:
+        start = timeit.default_timer()
+        for _ in range(1):
+            for col, t in enumerate(tests):
+                sol = executor()
+                result = sol.threeNumberSum(t[0], t[1])
+                exp = t[2]
+                assert result == exp, (
+                    f"\033[93m» {result} <> {exp}\033[91m for"
+                    + f" test {col} using \033[1m{executor.__name__}"
+                )
+        stop = timeit.default_timer()
+        used = str(round(stop - start, 5))
+        cols = "{0:20}{1:10}{2:10}"
+        res = cols.format(executor.__name__, used, "seconds")
+        print(f"\033[92m» {res}\033[0m")
+
+
+test()