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ⓁⒸ ‧‧‧ 896. Monotonic Array

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單調的陣列

896. Monotonic Array

❀ Origin

Problem

An array is monotonic if it is either monotone increasing or monotone decreasing.
An array A is monotone increasing if for all i <= j, A[i] <= A[j].
An array A is monotone decreasing if for all i <= j, A[i] >= A[j].
Return true if and only if the given array A is monotonic.

Note

  1. 1 <= A.length <= 50000
  2. -100000 <= A[i] <= 100000

Example 1

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Input: [1,2,2,3]
Output: true

Example 2

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Input: [6,5,4,4]
Output: true

Example 3

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Input: [1,3,2]
Output: false

Example 4

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Input: [1,2,4,5]
Output: true

Example 5

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Input: [1,1,1]
Output: true

❀ 翻譯

問題

如果是單調的遞增或單調遞減，則這是個單調陣列
如果所有 i <= j, A[i] <= A[j] ，則 A 陣列為單調。
如果所有 i <= j, A[i] >= A[j] ，則 A 陣列為單調。
只有當給定的陣列 A 為單調時，才回傳 true 。

注意

  1. 1 <= A.length <= 50000
  2. -100000 <= A[i] <= 100000

❀ Solution

Golang

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package problem0896

/**
 * 判斷是否為單調的數列（統一遞增、遞減、不變）
 * 解題方向為：
 * 從 A 第一個數字，往後遍歷一次 A ，
 * 將當前數和之前一數字相比，判斷為增加還是減少，
 * 當 increasing, decreasing 都變成 false 時，
 * 則代表為不單調數列，故即可回傳 false
 * 都為單調即回傳 true
 */
func isMonotonic(A []int) bool {
	increasing, decreasing := true, true
	for i := 1; i < len(A); i++ {
		switch {
		case A[i] > A[i-1]:
			decreasing = false
		case A[i] < A[i-1]:
			increasing = false
		}

		if decreasing == false && increasing == false {
			return false
		}
	}
	return true
}