feat: solve combination sum

Author: Real-Reason

combination-sum/Real-Reason.kt

@@ -0,0 +1,23 @@
+package leetcode_study
+
+fun combinationSum(candidates: IntArray, target: Int): List<List<Int>> {
+    val result = mutableListOf<List<Int>>()
+    val nums = ArrayDeque<Int>()
+    dfs(candidates, target, 0, 0, nums, result)
+
+    return result
+}
+
+private fun dfs(candidates: IntArray, target: Int, startIdx: Int, total: Int, nums: ArrayDeque<Int>, result: MutableList<List<Int>>) {
+    if (target < total) return
+    if (target == total) {
+        result.add(ArrayList(nums))
+        return
+    }
+    for (i in startIdx..< candidates.size) {
+        val num = candidates[i]
+        nums.add(num)
+        dfs(candidates, target, i, total + num, nums, result)
+        nums.removeLast()
+    }
+}

product-of-array-except-self/Real-Reason.kt

@@ -26,4 +26,4 @@ fun productExceptSelf(nums: IntArray): IntArray {
     }
 
     return result.toIntArray()
-}
+}

two-sum/Real-Reason.kt

@@ -13,4 +13,4 @@ class `Real-Reason` {
         }
         throw RuntimeException("There is no solution")
     }
-}
+}