Commit ac81931

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solves #2784: Check if Array is Good in java

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`@@ -839,7 +839,7 @@`
`839`	`839`	`\| 2765 \| [Longest Alternating Subarray](https://leetcode.com/problems/longest-alternating-subarray) \| [![Java](assets/java.png)](src/LongestAlternatingSubarray.java) \| \|`
`840`	`840`	`\| 2769 \| [Find the Maximum Achievable Number](https://leetcode.com/problems/find-the-maximum-achievable-number) \| [![Java](assets/java.png)](src/FindTheMaximumAchievableNumber.java) \| \|`
`841`	`841`	`\| 2778 \| [Sum of Squares of Special Elements](https://leetcode.com/problems/sum-of-squares-of-special-elements) \| [![Java](assets/java.png)](src/SumOfSquaresOfSpecialElements.java) \| \|`
`842`		`-\| 2784 \| [Check if Array is Good](https://leetcode.com/problems/check-if-array-is-good) \| \| \|`
	`842`	`+\| 2784 \| [Check if Array is Good](https://leetcode.com/problems/check-if-array-is-good) \| [![Java](assets/java.png)](src/CheckIfArrayIsGood.java) \| \|`
`843`	`843`	`\| 2788 \| [Split Strings by Separator](https://leetcode.com/problems/split-strings-by-separator) \| \| \|`
`844`	`844`	`\| 2798 \| [Number of Employees Who Met the Target](https://leetcode.com/problems/number-of-employees-who-met-the-target) \| \| \|`
`845`	`845`	`\| 2806 \| [Account Balance After Rounded Purchase](https://leetcode.com/problems/account-balance-after-rounded-purchase) \| \| \|`

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	`1`	`+// https://leetcode.com/problems/check-if-array-is-good`
	`2`	`+// T: O(N)`
	`3`	`+// S: O(N)`
	`4`	`+`
	`5`	`+import java.util.HashMap;`
	`6`	`+import java.util.Map;`
	`7`	`+`
	`8`	`+public class CheckIfArrayIsGood {`
	`9`	`+ public boolean isGood(int[] array) {`
	`10`	`+ final Map<Integer, Integer> frequencies = getFrequencies(array);`
	`11`	`+ for (int i = 1 ; i < array.length - 1 ; i++) {`
	`12`	`+ if (frequencies.getOrDefault(i, 0) != 1) {`
	`13`	`+ return false;`
	`14`	`+ }`
	`15`	`+ }`
	`16`	`+ return frequencies.getOrDefault(array.length - 1, 0) == 2;`
	`17`	`+ }`
	`18`	`+`
	`19`	`+ private Map<Integer, Integer> getFrequencies(int[] array) {`
	`20`	`+ final Map<Integer, Integer> result = new HashMap<>();`
	`21`	`+ for (int element : array) {`
	`22`	`+ result.put(element, result.getOrDefault(element, 0) + 1);`
	`23`	`+ }`
	`24`	`+ return result;`
	`25`	`+ }`
	`26`	`+}`

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