feat: solve product Except self

Author: Real-Reason

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

@@ -0,0 +1,29 @@
+package leetcode_study
+
+fun productExceptSelf(nums: IntArray): IntArray {
+    // ex. nums = [1, 2, 3, 4]
+    val leftStartProducts = mutableListOf(1)
+    val rightStartProducts = mutableListOf(1)
+
+    // mutableNums = [1, 1, 2, 3, 4]
+    val mutableNums = nums.toMutableList()
+    mutableNums.add(0, 1)
+    mutableNums.add(1)
+
+    // leftStartProducts = [1, 1, 2, 6, 24, 24]
+    // rightStartProducts = [24, 24, 24, 12, 4, 1]
+    for (idx in 1..< mutableNums.size) {
+        val leftNum = mutableNums[idx]
+        val rightNum = mutableNums[mutableNums.size - 1 - idx]
+
+        leftStartProducts.add(leftStartProducts.last() * leftNum)
+        rightStartProducts.add(index = 0, element = rightStartProducts.first() * rightNum)
+    }
+
+    val result = mutableListOf<Int>()
+    for (idx in 0..mutableNums.size - 3) {
+        result.add(leftStartProducts[idx] * rightStartProducts[idx + 2])
+    }
+
+    return result.toIntArray()
+}