python3/ADD: 189.旋转数组.py

双指针、数组、数学

Author: menghuu

python3/189.旋转数组.py

@@ -0,0 +1,101 @@
+#! /usr/bin/env python
+# -*- coding: utf-8 -*-
+# vim:fenc=utf-8
+#
+# Created by m on 2021-09-11
+#
+
+"""
+
+"""
+
+from typing import List
+
+
+class Solution:
+    def rotate(self, nums: List[int], k: int) -> None:
+        """
+        Do not return anything, modify nums in-place instead.
+        """
+        # 分成两个部分，后一部分整体往前移动，前一部分整体拷贝到后面
+        # 前面一部分的index是[0, l - 1 - k] 或者说 [0, l - k)，或者说，长度是l-k, 那后一部分就是 [1-k, l)了，或者说长度是K
+
+        # 空间复杂度O(1)，时间复杂度O(n)
+        l = len(nums)
+        k %= l
+
+        start_index = 0
+        pre_index = start_index
+        pre_value = nums[pre_index]
+        swap_counts = 0
+        while True:
+            index = (pre_index + k) % l
+            pre_value, nums[index] = nums[index], pre_value
+            swap_counts += 1
+            if swap_counts == l:
+                break
+            else:
+                if index == start_index:
+                    start_index += 1
+                    pre_index = start_index
+                    pre_value = nums[pre_index]
+                else:
+                    pre_index = index
+
+        return
+
+        # 空间复杂度O(1), 时间复杂度O(n)
+        # -->+++> [0, l - k) [l-k, l)
+        # <+++<-- 翻转一次 [0, k) [k, l)          <===========这里的下标很重要
+        # +++><-- 前面反转
+        # +++>--> 后面反转
+
+        def reverse(nums, start=0, end=None):
+            # [start, end)
+            if end is None:
+                end = len(nums)
+            lo, hi = start, end - 1
+            while lo <= hi:
+                nums[lo], nums[hi] = nums[hi], nums[lo]
+                lo += 1
+                hi -= 1
+
+        l = len(nums)
+        k %= l
+
+        reverse(nums)
+        reverse(nums, 0, k)
+        reverse(nums, k, l)
+
+        return
+
+        # 空间复杂度O(n)，时间复杂度O(n)
+        l = len(nums)
+        k %= l
+        tmp = nums[:l-k][:]
+        for i in range(l - k, l):
+            nums[i - (l - k)] = nums[i]
+        for i in range(k, l):
+            nums[i] = tmp[i - k]
+        return
+
+        # 空间复杂度O(n)，时间复杂度O(n)
+        l = len(nums)
+        k %= l
+        ans = [None] * l
+        for i, num in enumerate(nums):
+            ans[(i + k) % l] = num
+        nums[:] = ans[:]
+
+
+if __name__ == '__main__':
+    so = Solution()
+    nums = [1, 2, 3, 4, 5, 6, 7]
+    k = 3
+    nums = [1, 2, 3, 4, 5]
+    k = 2
+    # nums = [-1, -100, 3, 99]
+    # k = 2
+    so.rotate(nums, k)
+    print(nums)
+    pass