594. Longest Harmonious Subsequence 最长的和谐子序列

Posted 2020-09-23 Long Long Journey

• Total Accepted: 5540
• Total Submissions: 14066
• Difficulty: Easy
• Contributors:love_Fawn

We define a harmonious array is an array where the difference between its maximum value and its minimum value is exactly 1.

Now, given an integer array, you need to find the length of its longest harmonious subsequence among all its possible subsequences.

Example 1:

Input: [1,3,2,2,5,2,3,7]
Output: 5
Explanation: The longest harmonious subsequence is [3,2,2,2,3].

Note: The length of the input array will not exceed 20,000.

一种最大值和最小值相差1的数组，叫做和谐数组，求最大和谐子序列的长度

public class Solution {
    public int FindLHS(int[] nums) {
		if (nums.Length == 0) {
			return 0;
		}
		Array.Sort(nums);
		Dictionary<int, int> dict = new Dictionary<int, int>();
		for(int i = 0; i < nums.Length; i++) {
			int num = nums[i];
			int val = 0;
			dict.TryGetValue(num, out val);
			if (val > 0) {
				dict[num]++;
			} else {
				dict[num] = 1;
			}
		}
		int sum = 0;
		int? lastKey = null;
		foreach(int i in dict.Keys) {
			if (lastKey == null) {
				lastKey = i;
				continue;
			}
			int lk = (int)lastKey;
			if (Math.Abs(i - lk) == 1) {
				sum = Math.Max(sum, dict[i] + dict[lk]);
			}
			lastKey = i;
		}
		return sum;
    }
}

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