[leetcode]594. Longest Harmonious Subsequence

最新推荐文章于 2019-12-30 05:29:57 发布

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本文介绍了一种寻找整数数组中最长和谐子序列的方法。和谐子序列定义为数组中最大值与最小值之差恰好为1的子序列。通过排序数组并使用哈希映射记录每个元素出现的次数，算法能有效地找出符合条件的最长子序列。

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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].

思路：定义一个map，记录数组中数字出现的次数，连续两个数字出现次数的和即为harmonious subsequence。在求最大的harmonious subsequence.

Solution:

package com.billkang;

import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.Map;

/**
 * @author binkang
 * @date May 21, 2017
 */
public class LongestHarmoniousSubsequence {

	public int findLHS(int[] nums) {
		if(nums.length<1) return 0;
		Arrays.sort(nums);
		Map<Integer, Integer> map = new LinkedHashMap<Integer, Integer>();
		for (int i = 0; i < nums.length; i++) {
			if (map.get(nums[i]) == null) {
				map.put(nums[i], 1);
			} else {
				int temp = map.get(nums[i]);
				map.put(nums[i], temp + 1);
			}
		}
		
		
		int beforeKey = 0;
		int beforeValue = 0;
		int result = 0;
		for(Map.Entry<Integer, Integer> entry:map.entrySet()) {
			if(beforeValue == 0) {
				beforeKey = entry.getKey();
				beforeValue = entry.getValue();
			} else {
				if(entry.getKey()-beforeKey == 1) {
					result = Math.max(beforeValue+entry.getValue(), result);
				}
				beforeKey = entry.getKey();
				beforeValue = entry.getValue();
			}
		}
		return result;
		
	}
}