2023-08-31 Daily Challenge

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Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 31

Description

Minimum Number of Taps to Open to Water a Garden

There is a one-dimensional garden on the x-axis. The garden starts at the point 0 and ends at the point n. (i.e The length of the garden is n).

There are n + 1 taps located at points [0, 1, ..., n] in the garden.

Given an integer n and an integer array ranges of length n + 1 where ranges[i] (0-indexed) means the i-th tap can water the area [i - ranges[i], i + ranges[i]] if it was open.

Return the minimum number of taps that should be open to water the whole garden, If the garden cannot be watered return -1.

 

Example 1:

Input: n = 5, ranges = [3,4,1,1,0,0]
Output: 1
Explanation: The tap at point 0 can cover the interval [-3,3]
The tap at point 1 can cover the interval [-3,5]
The tap at point 2 can cover the interval [1,3]
The tap at point 3 can cover the interval [2,4]
The tap at point 4 can cover the interval [4,4]
The tap at point 5 can cover the interval [5,5]
Opening Only the second tap will water the whole garden [0,5]

Example 2:

Input: n = 3, ranges = [0,0,0,0]
Output: -1
Explanation: Even if you activate all the four taps you cannot water the whole garden.

 

Constraints:

  • 1 <= n <= 104
  • ranges.length == n + 1
  • 0 <= ranges[i] <= 100

Solution

class Solution {
public:
  int minTaps(int n, vector<int>& ranges) {
    vector<int> right(n + 1);
    for(int i = 0; i <= n; ++i) {
      if(!ranges[i]) continue;
      int left = max(i - ranges[i], 0);
      if(right[left] < i + ranges[i]) {
        right[left] = i + ranges[i];
      }
    }
    int count = 0;
    int rightMost = 0;
    int end = 0;
    for(int i = 0; i <= n; ++i) {
      if(end < i) {
        if(rightMost <= end) return -1;
        end = rightMost;
        count += 1;
      }
      rightMost = max(rightMost, right[i]);
    }

    return count + (end < n);
  }
};

// Accepted
// 38/38 cases passed (14 ms)
// Your runtime beats 85.18 % of cpp submissions
// Your memory usage beats 55.15 % of cpp submissions (14.6 MB)
Algorithm