From eda4e207a3355ff01f729bf45fdd92902abc58f0 Mon Sep 17 00:00:00 2001
From: Matej Focko <me@mfocko.xyz>
Date: Sun, 11 Feb 2024 18:27:23 +0100
Subject: [PATCH] =?UTF-8?q?swift:=20add=20=C2=AB216.=20Combination=20Sum?=
 =?UTF-8?q?=20III=C2=BB?=
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Signed-off-by: Matej Focko <me@mfocko.xyz>
---
 swift/combination-sum-iii.swift | 40 +++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 swift/combination-sum-iii.swift

diff --git a/swift/combination-sum-iii.swift b/swift/combination-sum-iii.swift
new file mode 100644
index 0000000..633d11e
--- /dev/null
+++ b/swift/combination-sum-iii.swift
@@ -0,0 +1,40 @@
+class Solution {
+    private struct Solver {
+        let k, n: Int
+        var combinations: [[Int]]
+
+        init(k: Int, n: Int) {
+            self.k = k
+            self.n = n
+            self.combinations = []
+        }
+
+        mutating func solve() {
+            var combination: [Int] = []
+            solve(&combination, k: k, n: n, nextDigit: 1)
+        }
+
+        private mutating func solve(_ combination: inout [Int], k: Int, n: Int, nextDigit: Int) {
+            if k == 0 && n == 0 {
+                combinations.append(combination)
+                return
+            }
+
+            if k <= 0 || n <= 0 || nextDigit > 9 {
+                return
+            }
+
+            for d in nextDigit...9 {
+                combination.append(d)
+                solve(&combination, k: k - 1, n: n - d, nextDigit: d + 1)
+                _ = combination.popLast()
+            }
+        }
+    }
+
+    func combinationSum3(_ k: Int, _ n: Int) -> [[Int]] {
+        var s = Solver(k: k, n: n)
+        s.solve()
+        return s.combinations
+    }
+}