1326. Minimum Number of Taps to Open to Water a Garden

https://leetcode.com/problems/minimum-number-of-taps-to-open-to-water-a-garden

Description

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 <= 104

• ranges.length == n + 1

• 0 <= ranges[i] <= 100

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