Question

2055. Plates Between Candles

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Description

There is a long table with a line of plates and candles arranged on top of it. You are given a 0-indexed string s consisting of characters '*' and '|' only, where a '*' represents a plate and a '|' represents a candle.

You are also given a 0-indexed 2D integer array queries where queries[i] = [lefti, righti] denotes the substring s[lefti...righti] (inclusive). For each query, you need to find the number of plates between candles that are in the substring. A plate is considered between candles if there is at least one candle to its left and at least one candle to its right in the substring.

• For example, s = "||**||**|*", and a query [3, 8] denotes the substring "*||**|". The number of plates between candles in this substring is 2, as each of the two plates has at least one candle in the substring to its left and right.

Return _an integer array_ answer _where_ answer[i] _is the answer to the_ ith _query_.

 

Example 1:

Input: s = "**|**|***|", queries = [[2,5],[5,9]]
Output: [2,3]
Explanation:
- queries[0] has two plates between candles.
- queries[1] has three plates between candles.

Example 2:

Input: s = "***|**|*****|**||**|*", queries = [[1,17],[4,5],[14,17],[5,11],[15,16]]
Output: [9,0,0,0,0]
Explanation:
- queries[0] has nine plates between candles.
- The other queries have zero plates between candles.

 

Constraints:

• 3 <= s.length <= 105
• s consists of '*' and '|' characters.
• 1 <= queries.length <= 105
• queries[i].length == 2
• 0 <= lefti <= righti < s.length

Solutions

Solution 1

class Solution:
  def platesBetweenCandles(self, s: str, queries: List[List[int]]) -> List[int]:
    n = len(s)
    presum = [0] * (n + 1)
    for i, c in enumerate(s):
      presum[i + 1] = presum[i] + (c == '*')

    left, right = [0] * n, [0] * n
    l = r = -1
    for i, c in enumerate(s):
      if c == '|':
        l = i
      left[i] = l
    for i in range(n - 1, -1, -1):
      if s[i] == '|':
        r = i
      right[i] = r

    ans = [0] * len(queries)
    for k, (l, r) in enumerate(queries):
      i, j = right[l], left[r]
      if i >= 0 and j >= 0 and i < j:
        ans[k] = presum[j] - presum[i + 1]
    return ans

class Solution {
  public int[] platesBetweenCandles(String s, int[][] queries) {
    int n = s.length();
    int[] presum = new int[n + 1];
    for (int i = 0; i < n; ++i) {
      presum[i + 1] = presum[i] + (s.charAt(i) == '*' ? 1 : 0);
    }
    int[] left = new int[n];
    int[] right = new int[n];
    for (int i = 0, l = -1; i < n; ++i) {
      if (s.charAt(i) == '|') {
        l = i;
      }
      left[i] = l;
    }
    for (int i = n - 1, r = -1; i >= 0; --i) {
      if (s.charAt(i) == '|') {
        r = i;
      }
      right[i] = r;
    }
    int[] ans = new int[queries.length];
    for (int k = 0; k < queries.length; ++k) {
      int i = right[queries[k][0]];
      int j = left[queries[k][1]];
      if (i >= 0 && j >= 0 && i < j) {
        ans[k] = presum[j] - presum[i + 1];
      }
    }
    return ans;
  }
}

class Solution {
public:
  vector<int> platesBetweenCandles(string s, vector<vector<int>>& queries) {
    int n = s.size();
    vector<int> presum(n + 1);
    for (int i = 0; i < n; ++i) presum[i + 1] = presum[i] + (s[i] == '*');
    vector<int> left(n);
    vector<int> right(n);
    for (int i = 0, l = -1; i < n; ++i) {
      if (s[i] == '|') l = i;
      left[i] = l;
    }
    for (int i = n - 1, r = -1; i >= 0; --i) {
      if (s[i] == '|') r = i;
      right[i] = r;
    }
    vector<int> ans(queries.size());
    for (int k = 0; k < queries.size(); ++k) {
      int i = right[queries[k][0]];
      int j = left[queries[k][1]];
      if (i >= 0 && j >= 0 && i < j) ans[k] = presum[j] - presum[i + 1];
    }
    return ans;
  }
};

func platesBetweenCandles(s string, queries [][]int) []int {
  n := len(s)
  presum := make([]int, n+1)
  for i := range s {
    if s[i] == '*' {
      presum[i+1] = 1
    }
    presum[i+1] += presum[i]
  }
  left, right := make([]int, n), make([]int, n)
  for i, l := 0, -1; i < n; i++ {
    if s[i] == '|' {
      l = i
    }
    left[i] = l
  }
  for i, r := n-1, -1; i >= 0; i-- {
    if s[i] == '|' {
      r = i
    }
    right[i] = r
  }
  ans := make([]int, len(queries))
  for k, q := range queries {
    i, j := right[q[0]], left[q[1]]
    if i >= 0 && j >= 0 && i < j {
      ans[k] = presum[j] - presum[i+1]
    }
  }
  return ans
}