[LTC] Lv2 / Elimination Game / 7분

leetcode/0chnxxx/Elimination_Game.kt

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+/**
+ * You have a list arr of all integers in the range [1, n] sorted in a strictly increasing order. Apply the following algorithm on arr:
+ * Starting from left to right, remove the first number and every other number afterward until you reach the end of the list.
+ * Repeat the previous step again, but this time from right to left, remove the rightmost number and every other number from the remaining numbers.
+ * Keep repeating the steps again, alternating left to right and right to left, until a single number remains.
+ * Given the integer n, return the last number that remains in arr.
+ *
+ * Constraints:
+ * 1 <= n <= 10^9
+ */
+
+fun main() {
+    val n = 9
+
+    val result = Solution().lastRemaining(n)
+
+    println(result)
+}
+
+class Solution {
+    // 시간 복잡도 : O(log N)
+    // 공간 복잡도 : O(1)
+    fun lastRemaining(n: Int): Int {
+        var head = 1
+        var step = 1
+        var remaining = n
+        var leftToRight = true
+
+        while (remaining > 1) {
+            if (leftToRight || remaining % 2 == 1) {
+                head += step
+            }
+
+            remaining /= 2
+            step *= 2
+            leftToRight = !leftToRight
+        }
+
+        return head
+    }
+}