update 565, cheathseet, progress

Author: yennanliu

README.md

@@ -218,7 +218,7 @@
 498 | [Diagonal Traverse](https://leetcode.com/problems/diagonal-traverse/) | [Python](./leetcode_python/Array/diagonal_traverse.py) | _O(n)_ | _O(1)_  | Medium |`matrix`,`google`,`fb`| AGAIN*** (3) (not start)
 531 | [Lonely Pixel I](https://leetcode.com/problems/lonely-pixel-i/) |  [Python](./leetcode_python/Array/lonely-pixel-i.py) | _O(m * n)_ | _O(m + n)_ | Medium | 🔒, `matrix`, `basic`| AGAIN*
 533 | [Lonely Pixel II](https://leetcode.com/problems/lonely-pixel-ii/) | [Python](./leetcode_python/Array/lonely-pixel-ii.py)  | _O(m * n)_ | _O(m * n)_ | Medium  |🔒| AGAIN (not start*)
-565 | [Array Nesting](https://leetcode.com/problems/array-nesting/) | [Python](./leetcode_python/Array/array-nesting.py) | _O(n)_ | _O(1)_ | Medium  |`apple`| AGAIN (not start)
+565 | [Array Nesting](https://leetcode.com/problems/array-nesting/) | [Python](./leetcode_python/Array/array-nesting.py) | _O(n)_ | _O(1)_ | Medium  |`union find`,`dfs`,`apple`| AGAIN**** (1)
 566 | [Reshape the Matrix](https://leetcode.com/problems/reshape-the-matrix/) | [Python](./leetcode_python/Array/reshape-the-matrix.py) | _O(m * n)_ | _O(m * n)_ | Easy |`basic`, `matrix`| AGAIN**
 581 | [Shortest Unsorted Continuous Subarray](https://leetcode.com/problems/shortest-unsorted-continuous-subarray/) | [Python](./leetcode_python/Array/shortest-unsorted-continuous-subarray.py) | _O(n)_ | _O(1)_ | Easy  |`basic`| AGAIN*
 605 | [Can Place Flowers](https://leetcode.com/problems/can-place-flowers/) | [Python](./leetcode_python/Array/can-place-flowers.py) | _O(n)_ | _O(1)_ | Easy |`pass vs continue`| OK*

data/progress.txt

@@ -1,3 +1,4 @@
+20220210: 565
 20220208: 670,406,1010,525,523
 20220207: 026,080,257,11,128
 20220206: 69,207,210

data/to_review.txt

@@ -1,3 +1,4 @@
+2022-04-06 -> ['565']
 2022-04-04 -> ['670,406,1010,525,523']
 2022-04-03 -> ['026,080,257,11,128']
 2022-04-02 -> ['69,207,210']
@@ -11,7 +12,7 @@
 2022-03-19 -> ['640']
 2022-03-18 -> ['553,606,662,295']
 2022-03-17 -> ['536,532']
-2022-03-16 -> ['532']
+2022-03-16 -> ['565', '532']
 2022-03-15 -> ['100,572,508']
 2022-03-14 -> ['670,406,1010,525,523']
 2022-03-13 -> ['026,080,257,11,128', '189,617']
@@ -24,27 +25,27 @@
 2022-03-06 -> ['190', '046,969,128']
 2022-03-05 -> ['235,236,1268', '658,005']
 2022-03-04 -> ['875,646,435,055']
-2022-03-03 -> ['1167', '508,663,725,278,035,875']
+2022-03-03 -> ['565', '1167', '508,663,725,278,035,875']
 2022-03-02 -> ['529,508']
 2022-03-01 -> ['670,406,1010,525,523', '406', '073,199']
 2022-02-28 -> ['026,080,257,11,128', '005,026,080,011']
 2022-02-27 -> ['69,207,210', '791']
 2022-02-26 -> ['640', '937,1041,994,523,525,204']
 2022-02-25 -> ['111,165,57,56,355', '553,606,662,295', '090,852,1131']
 2022-02-24 -> ['536,532']
-2022-02-23 -> ['532']
+2022-02-23 -> ['565', '532']
 2022-02-22 -> ['100,572,508']
 2022-02-21 -> ['670,406,1010,525,523', '190']
 2022-02-20 -> ['026,080,257,11,128', '235,236,1268', '189,617']
 2022-02-19 -> ['69,207,210', '560,264,703']
-2022-02-18 -> ['1167', '1010,134,089']
+2022-02-18 -> ['565', '1167', '1010,134,089']
 2022-02-17 -> ['111,165,57,56,355', '647']
 2022-02-16 -> ['670,406,1010,525,523', '406', '323,008,538']
-2022-02-15 -> ['026,080,257,11,128', '005,026,080,011', '716,136,163,725,621']
+2022-02-15 -> ['565', '026,080,257,11,128', '005,026,080,011', '716,136,163,725,621']
 2022-02-14 -> ['69,207,210', '791', '57,56,227,224']
-2022-02-13 -> ['670,406,1010,525,523', '190', '640', '046,969,128']
-2022-02-12 -> ['026,080,257,11,128', '111,165,57,56,355', '235,236,1268', '553,606,662,295', '658,005']
-2022-02-11 -> ['670,406,1010,525,523', '69,207,210', '536,532', '875,646,435,055']
+2022-02-13 -> ['565', '670,406,1010,525,523', '190', '640', '046,969,128']
+2022-02-12 -> ['565', '026,080,257,11,128', '111,165,57,56,355', '235,236,1268', '553,606,662,295', '658,005']
+2022-02-11 -> ['565', '670,406,1010,525,523', '69,207,210', '536,532', '875,646,435,055']
 2022-02-10 -> ['670,406,1010,525,523', '026,080,257,11,128', '1167', '532', '508,663,725,278,035,875']
 2022-02-09 -> ['670,406,1010,525,523', '026,080,257,11,128', '69,207,210', '111,165,57,56,355', '100,572,508', '529,508']
 2022-02-08 -> ['026,080,257,11,128', '69,207,210', '190', '406', '073,199']

doc/cheatsheet/union_find.md

@@ -241,4 +241,26 @@ class Solution(object):
 ### 2-5) Friend Circles
 ```python
 # LC 547 Friend Circles
+```
+
+### 2-6) Array Nesting
+```python
+# LC 565. Array Nesting
+# V0
+# IDEA : UNION FIND
+class Solution(object):
+    def arrayNesting(self, nums):
+        def search(idx):
+            cnt = 0
+            while nums[idx] >= 0:
+                cnt += 1
+                next = nums[idx]
+                nums[idx] = -1
+                idx = next
+            return cnt
+        ans = 0
+        for x in range(len(nums)):
+            if nums[x] >= 0:
+                ans = max(ans, search(x))
+        return ans
 ```

doc/progress.md

@@ -1,12 +1,12 @@
 # Progress
 
-# 2022-02-09
+# 2022-02-10
 - DOING:
 	- LC (appl_)
 		- ref : https://github.com/yennanliu/CS_basics/blob/master/doc/leetcode_company_V1/Apple%20-%20LeetCode.pdf
 			- (pdf : p.2)
 				- 269
-				- 565
+				- 565 (ok, but again!!)
 	- ================
 		- LC (LC discuss sharing)
 			- https://leetcode.com/discuss/interview-question/1367526/apple-uber-flipkart-swiggy-interview-questions-july-2020-july-2021

leetcode_python/Array/array-nesting.py

@@ -37,28 +37,25 @@
 """
 
 # V0
-
-# V1 
-# https://blog.csdn.net/fuxuemingzhu/article/details/79460546
+# IDEA : UNION FIND
 class Solution(object):
     def arrayNesting(self, nums):
-        """
-        :type nums: List[int]
-        :rtype: int
-        """
-        visited = [False] * len(nums)
+        def search(idx):
+            cnt = 0
+            while nums[idx] >= 0:
+                cnt += 1
+                next = nums[idx]
+                nums[idx] = -1
+                idx = next
+            return cnt
         ans = 0
-        for i in range(len(nums)):
-            road = 0
-            while not visited[i]:
-                road += 1
-                # order of below 2 lines of code is unchangeable
-                visited[i] = True
-                i = nums[i]
-            ans = max(ans, road)
+        for x in range(len(nums)):
+            if nums[x] >= 0:
+                ans = max(ans, search(x))
         return ans
 
-# V1'
+# V1
+# IDEA : UNION FIND
 # http://bookshadow.com/weblog/2017/05/28/leetcode-array-nesting/
 class Solution(object):
     def arrayNesting(self, nums):
@@ -80,6 +77,168 @@ def search(idx):
                 ans = max(ans, search(x))
         return ans
 
+# V1'
+# IDEA : UNION FIND
+# https://blog.csdn.net/fuxuemingzhu/article/details/79460546
+class Solution(object):
+    def arrayNesting(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        visited = [False] * len(nums)
+        ans = 0
+        for i in range(len(nums)):
+            road = 0
+            while not visited[i]:
+                road += 1
+                # order of below 2 lines of code is unchangeable
+                visited[i] = True
+                i = nums[i]
+            ans = max(ans, road)
+        return ans
+
+# V1''
+# IDEA : UNION FIND
+# https://leetcode.com/problems/array-nesting/discuss/209108/Python-solution
+class Solution(object):
+    def arrayNesting(self, nums):
+        seen = [0]*len(nums)
+        res = 0
+        for i in range(len(nums)):
+            if seen[i] != -1:
+                j = i
+                count = 0
+                while seen[j] != -1:
+                    count += 1
+                    seen[j] = -1
+                    j = nums[j]
+                res = max(res, count)
+        return res
+
+# V1'''
+# IDEA : optimzied (we don't need extra space for seen, just make nums[idx] as -1)
+# https://leetcode.com/problems/array-nesting/discuss/209108/Python-solution
+class Solution(object):
+    def arrayNesting(self, nums):
+        res = 0
+        for i in range(len(nums)):
+            if nums[i] != -1:
+                j = i
+                count = 0
+                while nums[j] != -1:
+                    count += 1
+                    tmp = nums[j]
+                    nums[j] = -1
+                    j = tmp
+                res = max(res, count)
+        return res
+
+# V1''''
+# IDEA : UNION FIND
+# https://leetcode.com/problems/array-nesting/discuss/1439139/AA-Python-solution
+class Solution:
+    def arrayNesting(self, nums):
+        res = 0
+        seen = set()
+        for i in range(len(nums)):
+            if nums[i] not in seen:
+                tmp = self.build(nums, i)
+                seen |= tmp
+                res = max(res, len(tmp))
+        return res     
+        
+    def build(self, nums, k):
+        res = set()
+        current = nums[k]
+        while current not in res:
+            res.add(current)
+            current = nums[current]
+        return res
+
+# V1'''''
+# https://leetcode.com/problems/array-nesting/discuss/314782/python
+class Solution:
+    def arrayNesting(self, nums):
+        res = 0
+        visited = [0] * len(nums)
+        for i in range(len(nums)):
+            cur, cur_res = i, 0
+            while not visited[cur]:
+                visited[cur] = 1
+                cur_res += 1
+                cur = nums[cur]
+            res = max(res, cur_res)
+        return res
+
+# V1''''''
+# IDEA : BRUTE FORCE (time out error)
+# https://leetcode.com/problems/array-nesting/solution/
+# JAVA
+# public class Solution {
+#     public int arrayNesting(int[] nums) {
+#         int res = 0;
+#         for (int i = 0; i < nums.length; i++) {
+#             int start = nums[i], count = 0;
+#             do {
+#                 start = nums[start];
+#                 count++;
+#             }
+#             while (start != nums[i]);
+#             res = Math.max(res, count);
+#
+#         }
+#         return res;
+#     }
+# }
+
+# V1''''''
+# IDEA : VISITED ARRAY
+# JAVA
+# https://leetcode.com/problems/array-nesting/solution/
+# public class Solution {
+#     public int arrayNesting(int[] nums) {
+#         boolean[] visited = new boolean[nums.length];
+#         int res = 0;
+#         for (int i = 0; i < nums.length; i++) {
+#             if (!visited[i]) {
+#                 int start = nums[i], count = 0;
+#                 do {
+#                     start = nums[start];
+#                     count++;
+#                     visited[start] = true;
+#                 }
+#                 while (start != nums[i]);
+#                 res = Math.max(res, count);
+#             }
+#         }
+#         return res;
+#     }
+# }
+
+# V1''''''''
+# IDEA : VISITED ARRAY WITHOUT EXTRA SPACE
+# https://leetcode.com/problems/array-nesting/solution/
+# JAVA
+# public class Solution {
+#     public int arrayNesting(int[] nums) {
+#         int res = 0;
+#         for (int i = 0; i < nums.length; i++) {
+#             if (nums[i] != Integer.MAX_VALUE) {
+#                 int start = nums[i], count = 0;
+#                 while (nums[start] != Integer.MAX_VALUE) {
+#                     int temp = start;
+#                     start = nums[start];
+#                     count++;
+#                     nums[temp] = Integer.MAX_VALUE;
+#                 }
+#                 res = Math.max(res, count);
+#             }
+#         }
+#         return res;
+#     }
+# }
+
 # V2 
 # Time:  O(n)
 # Space: O(1)