Add combination sum solution

Author: hyunjung-choi

combination-sum/hyunjung-choi.kt

@@ -0,0 +1,43 @@
+class Solution {
+    fun combinationSum(candidates: IntArray, target: Int): List<List<Int>> {
+        val result = mutableListOf<List<Int>>()
+        val currentCombination = mutableListOf<Int>()
+
+        candidates.sort()
+
+        backtrack(candidates, target, 0, currentCombination, result)
+
+        return result
+    }
+
+    private fun backtrack(
+        candidates: IntArray,
+        remainingTarget: Int,
+        startIndex: Int,
+        currentCombination: MutableList<Int>,
+        result: MutableList<List<Int>>
+    ) {
+        if (remainingTarget == 0) {
+            result.add(currentCombination.toList())
+            return
+        }
+
+        if (remainingTarget < 0) {
+            return
+        }
+
+        for (i in startIndex until candidates.size) {
+            val candidate = candidates[i]
+
+            if (candidate > remainingTarget) {
+                break
+            }
+
+            currentCombination.add(candidate)
+
+            backtrack(candidates, remainingTarget - candidate, i, currentCombination, result)
+
+            currentCombination.removeAt(currentCombination.size - 1)
+        }
+    }
+}