[LTC] Lv2 / Random Pick Index / 5분

leetcode/0chnxxx/Random_Pick_Index.kt

@@ -0,0 +1,43 @@
+/**
+ * Given an integer array nums with possible duplicates, randomly output the index of a given target number.
+ * You can assume that the given target number must exist in the array.
+ *
+ * Implement the Solution class:
+ * Solution(int[] nums) Initializes the object with the array nums.
+ * int pick(int target) Picks a random index i from nums where nums[i] == target.
+ * If there are multiple valid i's, then each index should have an equal probability of returning.
+ *
+ * Constraints:
+ * 1 <= nums.length <= 2 * 10^4
+ * -2^31 <= nums[i] <= 2^31 - 1
+ * target is an integer from nums.
+ * At most 10^4 calls will be made to pick.
+ */
+
+fun main() {
+    val solution = Solution(intArrayOf(1, 2, 3, 3, 3));
+    println(solution.pick(3))
+    println(solution.pick(1))
+    println(solution.pick(3))
+}
+
+class Solution(private val nums: IntArray) {
+    // 시간 복잡도 : O(N)
+    // 공간 복잡도 : O(1)
+    fun pick(target: Int): Int {
+        var result = -1
+        var count = 0
+
+        for (i in nums.indices) {
+            if (nums[i] == target) {
+                count++
+
+                if ((0 until count).random() == 0) {
+                    result = i
+                }
+            }
+        }
+
+        return result
+    }
+}