{"id":7312,"date":"2020-08-29T22:44:48","date_gmt":"2020-08-30T05:44:48","guid":{"rendered":"https:\/\/zxi.mytechroad.com\/blog\/?p=7312"},"modified":"2020-08-29T22:45:16","modified_gmt":"2020-08-30T05:45:16","slug":"leetcode-1566-detect-pattern-of-length-m-repeated-k-or-more-times","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/algorithms\/array\/leetcode-1566-detect-pattern-of-length-m-repeated-k-or-more-times\/","title":{"rendered":"\u82b1\u82b1\u9171 LeetCode 1566. Detect Pattern of Length M Repeated K or More Times"},"content":{"rendered":"\n

Given an array of positive integers arr<\/code>,  find a pattern of length m<\/code> that is repeated k<\/code> or more times.<\/p>\n\n\n\n

A pattern<\/strong> is a subarray (consecutive sub-sequence) that consists of one or more values, repeated multiple times consecutively <\/strong>without overlapping. A pattern is defined by its length and the number of repetitions.<\/p>\n\n\n\n

Return true<\/code> if there exists a pattern of length<\/em> m<\/code> that is repeated<\/em> k<\/code> or more times, otherwise return<\/em> false<\/code>.<\/p>\n\n\n\n

Example 1:<\/strong><\/p>\n\n\n\n

Input:<\/strong> arr = [1,2,4,4,4,4], m = 1, k = 3\nOutput:<\/strong> true\nExplanation: <\/strong>The pattern (4)<\/strong> of length 1 is repeated 4 consecutive times. Notice that pattern can be repeated k or more times but not less.\n<\/pre>\n\n\n\n
Example 2:<\/strong><\/p>\n\n\n\n
Input:<\/strong> arr = [1,2,1,2,1,1,1,3], m = 2, k = 2\nOutput:<\/strong> true\nExplanation: <\/strong>The pattern (1,2)<\/strong> of length 2 is repeated 2 consecutive times. Another valid pattern (2,1) is<\/strong> also repeated 2 times.\n<\/pre>\n\n\n\n
Example 3:<\/strong><\/p>\n\n\n\n
Input:<\/strong> arr = [1,2,1,2,1,3], m = 2, k = 3\nOutput:<\/strong> false\nExplanation: <\/strong>The pattern (1,2) is of length 2 but is repeated only 2 times. There is no pattern of length 2 that is repeated 3 or more times.\n<\/pre>\n\n\n\n
Example 4:<\/strong><\/p>\n\n\n\n
Input:<\/strong> arr = [1,2,3,1,2], m = 2, k = 2\nOutput:<\/strong> false\nExplanation: <\/strong>Notice that the pattern (1,2) exists twice but not consecutively, so it doesn't count.\n<\/pre>\n\n\n\n
Example 5:<\/strong><\/p>\n\n\n\n
Input:<\/strong> arr = [2,2,2,2], m = 2, k = 3\nOutput:<\/strong> false\nExplanation: <\/strong>The only pattern of length 2 is (2,2) however it's repeated only twice. Notice that we do not count overlapping repetitions.\n<\/pre>\n\n\n\n
Constraints:<\/strong><\/p>\n\n\n\n
  • 2 <= arr.length <= 100<\/code><\/li>
  • 1 <= arr[i] <= 100<\/code><\/li>
  • 1 <= m <= 100<\/code><\/li>
  • 2 <= k <= 100<\/code><\/li><\/ul>\n\n\n\n
    Solution 1: Brute Force<\/strong><\/h2>\n\n\n\n
    Time complexity: O(nmk)
    Space complexity: O(1)<\/p>\n\n\n\n
    \n
    C++<\/h2>\n
    \n\n
    \nclass Solution {\npublic:\n  bool containsPattern(vector& arr, int m, int k) {\n    const int n = arr.size();\n    for (int i = 0; i + m * k <= n; ++i) {\n      bool valid = true;\n      for (int j = 1; j < k && valid; ++j)\n        for (int p = 0; p < m && valid; ++p)\n          if (arr[i + j * m + p] != arr[i + p])\n            valid = false;\n      if (valid) return true;\n    }\n    return false;\n  }\n};\n<\/pre>\n<\/div><\/div>\n\n\n\n
    Solution 2: Shift and count<\/strong><\/h2>\n\n\n\n
    Since we need k consecutive subarrays, we can compare arr[i] with arr[i + m], if they are the same, increase the counter, otherwise reset the counter. If the counter reaches (k - 1)  * m, it means we found k consecutive subarrays of length m.<\/p>\n\n\n\n
    ex1: arr = [1,2,4,4,4,4], m = 1, k = 3
    i arr[i], arr[i + m] counter
    0 1.       2.               0
    0 2.       4.               0
    0 4.       4.               1
    0 4.       4.               2. <-- found<\/p>\n\n\n\n
    ex2: arr = [1,2,1,2,1,1,1,3], m = 2, k = 2
    i arr[i], arr[i + m] counter
    0 1.       1.               1
    0 2.       2.               2 <-- found<\/p>\n\n\n\n
    Time complexity: O(n)
    Space complexity: O(1)<\/p>\n\n\n\n
    \n
    C++<\/h2>\n
    \n\n
    \nclass Solution {\npublic:\n  bool containsPattern(vector& arr, int m, int k) {\n    const int n = arr.size();\n    int count = 0;\n    for (int i = 0; i + m < n; ++i) {      \n      if (arr[i] == arr[i + m]) {\n        if (++count == (k - 1) * m) return true;\n      } else {\n        count = 0;\n      }      \n    }\n    return false;\n  }\n};\n<\/pre>\n<\/div><\/div>\n\n\n\n
    <\/p>\n","protected":false},"excerpt":{"rendered":"
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