[Swift]LeetCode1326. 灌溉花園的最少水龍頭數目 | Minimum Number of Taps to Open to Water a Garden

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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.
Example 3:

Input: n = 7, ranges = [1,2,1,0,2,1,0,1]
Output: 3
Example 4:

Input: n = 8, ranges = [4,0,0,0,0,0,0,0,4]
Output: 2
Example 5:

Input: n = 8, ranges = [4,0,0,0,4,0,0,0,4]
Output: 1
 

Constraints:

1 <= n <= 10^4
ranges.length == n + 1
0 <= ranges[i] <= 100

---

在 x 軸上有一個一維的花園。花園長度為 n，從點 0 開始，到點 n 結束。

花園里總共有 n + 1 個水龍頭，分別位於 [0, 1, ..., n] 。

給你一個整數 n 和一個長度為 n + 1 的整數數組 ranges ，其中 ranges[i] （下標從 0 開始）表示：如果打開點 i 處的水龍頭，可以灌溉的區域為 [i -  ranges[i], i + ranges[i]] 。

請你返回可以灌溉整個花園的 最少水龍頭數目 。如果花園始終存在無法灌溉到的地方，請你返回 -1 。

 

示例 1：

 

 

 

輸入：n = 5, ranges = [3,4,1,1,0,0]
輸出：1
解釋：
點 0 處的水龍頭可以灌溉區間 [-3,3]
點 1 處的水龍頭可以灌溉區間 [-3,5]
點 2 處的水龍頭可以灌溉區間 [1,3]
點 3 處的水龍頭可以灌溉區間 [2,4]
點 4 處的水龍頭可以灌溉區間 [4,4]
點 5 處的水龍頭可以灌溉區間 [5,5]
只需要打開點 1 處的水龍頭即可灌溉整個花園 [0,5] 。
示例 2：

輸入：n = 3, ranges = [0,0,0,0]
輸出：-1
解釋：即使打開所有水龍頭，你也無法灌溉整個花園。
示例 3：

輸入：n = 7, ranges = [1,2,1,0,2,1,0,1]
輸出：3
示例 4：

輸入：n = 8, ranges = [4,0,0,0,0,0,0,0,4]
輸出：2
示例 5：

輸入：n = 8, ranges = [4,0,0,0,4,0,0,0,4]
輸出：1
 

提示：

1 <= n <= 10^4
ranges.length == n + 1
0 <= ranges[i] <= 100

---

Runtime: 148 ms

Memory Usage: 21.7 MB

class Solution {
    func minTaps(_ n: Int, _ ranges: [Int]) -> Int {
        var rg:[[Int]] = [[Int]](repeating: [Int](repeating: 0, count: 2), count: n + 1)
        for i in 0...n
        {
            let s:Int =  i - ranges[i]
            let e:Int =  i + ranges[i]
            rg[i] = [s < 0 ? 0 : s, e < n ? e : n]
        }
        rg = rg.sorted(by:{
            if $0[0] == $1[0]
            {
                return $0[1] < $1[1]
            }
            else
            {
                return $0[0] < $1[0]
            }
        }
        )
        var ans:Int = 0
        var i:Int = 0
        var start:Int = 0
        var end:Int = 0
        while(start < n && i <= n)
        {
            while(i <= n && rg[i][0] <= start)
            {
                end = max(end, rg[i][1])
                i += 1
            }
            if end <= start{return -1}
            start = end
            ans += 1
        }
        return ans
    }
}