2021-06-29 Daily-Challenge

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Today I have done Construct the Lexicographically Largest Valid Sequence and leetcode's June LeetCoding Challenge with cpp.

Construct the Lexicographically Largest Valid Sequence

Description

Given an integer n, find a sequence that satisfies all of the following:

  • The integer 1 occurs once in the sequence.
  • Each integer between 2 and n occurs twice in the sequence.
  • For every integer i between 2 and n, the distance between the two occurrences of i is exactly i.

The distance between two numbers on the sequence, a[i] and a[j], is the absolute difference of their indices, |j - i|.

Return the lexicographically largest sequence*. It is guaranteed that under the given constraints, there is always a solution.*

A sequence a is lexicographically larger than a sequence b (of the same length) if in the first position where a and b differ, sequence a has a number greater than the corresponding number in b. For example, [0,1,9,0] is lexicographically larger than [0,1,5,6] because the first position they differ is at the third number, and 9 is greater than 5.

Example 1:

Input: n = 3
Output: [3,1,2,3,2]
Explanation: [2,3,2,1,3] is also a valid sequence, but [3,1,2,3,2] is the lexicographically largest valid sequence.

Example 2:

Input: n = 5
Output: [5,3,1,4,3,5,2,4,2]

Constraints:

  • 1 <= n <= 20

Solution

class Solution {
  vector<bool> vis;
  vector<int> answer;
  int n;
  bool solve(int index) {
    if(index == 2 * n - 1) return true;
    // cout << "#" << answer << endl;
    if(answer[index]) return solve(index + 1);
    for(int i = min(n, 2 * n - 2 - index); i > 1 ; --i) {
      // cout << index << ' ' << i << endl;
      if(vis[i]) continue;
      // cout << "???" << endl;
      if(i != 1 && answer[i + index]) continue;
      // cout << "????" << endl;
      answer[index] = i;
      answer[index + i] = i;
      vis[i] = true;
      if(solve(index + 1)) return true;
      answer[index] = 0;
      answer[index + i] = 0;
      vis[i] = false;
    }
    if(!vis[1]) {
      answer[index] = 1;
      vis[1] = true;
      if(solve(index + 1)) return true;
      vis[1] = false;
      answer[index] = 0;
    }
    return false;
  }
public:
  vector<int> constructDistancedSequence(int n) {
    this->n = n;
    vis.resize(n + 1);
    answer.resize(n * 2 - 1);
    solve(0);
    return answer;
  }
};

June LeetCoding Challenge 29

Description

Max Consecutive Ones III

Given a binary array nums and an integer k, return the maximum number of consecutive 1's in the array if you can flip at most k 0's.

Example 1:

Input: nums = [1,1,1,0,0,0,1,1,1,1,0], k = 2
Output: 6
Explanation: [1,1,1,0,0,1,1,1,1,1,1]
Bolded numbers were flipped from 0 to 1. The longest subarray is underlined.

Example 2:

Input: nums = [0,0,1,1,0,0,1,1,1,0,1,1,0,0,0,1,1,1,1], k = 3
Output: 10
Explanation: [0,0,1,1,1,1,1,1,1,1,1,1,0,0,0,1,1,1,1]
Bolded numbers were flipped from 0 to 1. The longest subarray is underlined.

Constraints:

  • 1 <= nums.length <= 10^5
  • nums[i] is either 0 or 1.
  • 0 <= k <= nums.length

Solution

[1,1,1,0,0,0,1,1,1,1,0]auto speedup = []() {
  std::ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  return nullptr;
}();
int ones[100000];
class Solution {
public:
  int longestOnes(vector<int>& nums, int k) {
    int len = nums.size();
    int answer = 0;
    int last = -1;
    int ed = 0;
    int start = 0;
    for(int i = 0; i < len; ++i) {
      if(!nums[i]) {
        if(!k) {
          last = i;
        } else {
          if(ed - start == k) last = ones[start++];
          ones[ed++] = i;
        }
      }
      // cout << i << ' ' << last << ' ' << ed << ' ' << start << endl;
      answer = max(answer, i - last);
    }
    return answer;
  }
};

// Accepted
// 48/48 cases passed (36 ms)
// Your runtime beats 99.56 % of cpp submissions
// Your memory usage beats 8.97 % of cpp submissions (55.6 MB)

auto speedup = []() {
  std::ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  return nullptr;
}();
class Solution {
public:
  int longestOnes(vector<int>& nums, int k) {
    int len = nums.size();
    int answer = 0;
    int last = -1;
    queue<int> q;
    for(int i = 0; i < len; ++i) {
      if(!nums[i]) {
        if(!k) {
          last = i;
        } else {
          if(q.size() == k) {
            last = q.front();
            q.pop();
          }
          q.push(i);
        }
      }
      // cout << i << ' ' << last << ' ' << ed << ' ' << start << endl;
      answer = max(answer, i - last);
    }
    return answer;
  }
};

// Accepted
// 48/48 cases passed (56 ms)
// Your runtime beats 59.23 % of cpp submissions
// Your memory usage beats 6.29 % of cpp submissions (57 MB)

auto speedup = []() {
  std::ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  return nullptr;
}();
class Solution {
public:
  int longestOnes(vector<int>& nums, int k) {
    int len = nums.size();
    int answer = 0;
    int last = -1;
    list<int> q;
    for(int i = 0; i < len; ++i) {
      if(!nums[i]) {
        if(!k) {
          last = i;
        } else {
          if(q.size() == k) {
            last = q.front();
            q.pop_front();
          }
          q.push_back(i);
        }
      }
      // cout << i << ' ' << last << ' ' << ed << ' ' << start << endl;
      answer = max(answer, i - last);
    }
    return answer;
  }
};

// Accepted
// 48/48 cases passed (68 ms)
// Your runtime beats 23.17 % of cpp submissions
// Your memory usage beats 5.15 % of cpp submissions (69.9 MB)

auto speedup = []() {
  std::ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  return nullptr;
}();
int ones[50000];
class Solution {
public:
  int longestOnes(vector<int>& nums, int k) {
    int s = accumulate(nums.begin(), nums.end(), 0);
    int len = nums.size();
    if(s + k >= len) return len;
    int answer = 0;
    int last = -1;
    int ed = 0;
    int start = 0;
    for(int i = 0; i < len; ++i) {
      if(!nums[i]) {
        if(!k) {
          last = i;
        } else {
          if(ed - start == k) last = ones[start++];
          ones[ed++] = i;
          start %= 50000;
          ed %= 50000;
        }
      }
      // cout << i << ' ' << last << ' ' << ed << ' ' << start << endl;
      answer = max(answer, i - last);
    }
    return answer;
  }
};

// Accepted
// 48/48 cases passed (28 ms)
// Your runtime beats 99.97 % of cpp submissions
// Your memory usage beats 8.97 % of cpp submissions (55.6 MB)
Algorithm