给定N个元素，编写一个程序，打印出相邻元素之差为1的最长递增子序列的长度。
例子：
Input : a[] = {3, 10, 3, 11, 4, 5, 6, 7, 8, 12}
Output : 6
Explanation: 3, 4, 5, 6, 7, 8 is the longest increasing subsequence whose adjacent element differs by one.
Input : a[] = {6, 7, 8, 3, 4, 5, 9, 10}
Output : 5
Explanation: 6, 7, 8, 9, 10 is the longest increasing subsequence
天真的方法：通常的方法是对每个元素进行迭代并找出最长的递增子序列。对于任何特定元素，请找到从该元素开始的子序列的长度。打印由此形成的子序列的最长长度。该方法的时间复杂度将为O(n 2 )。
动态编程方法：让DP [i]存储以A [i]结尾的最长子序列的长度。对于每个A [i]，如果在第i个索引之前的数组中存在A [i] -1，则A [i]将添加到具有A [i] -1的递增子序列中。因此， DP [i] = DP [index(A [i] -1)] +1 。如果在第i个索引之前的数组中不存在A [i] -1，则DP [i] = 1，因为A [i]元素形成了一个以A [i]开头的子序列。因此，DP [i]的关系为：
If A[i]-1 is present before i-th index:
- DP[i] = DP[ index(A[i]-1) ] + 1
else:
- DP[i] = 1
下面给出了上述方法的说明：
C++
// CPP program to find length of the
// longest increasing subsequence
// whose adjacent element differ by 1
#include
using namespace std;
// function that returns the length of the
// longest increasing subsequence
// whose adjacent element differ by 1
int longestSubsequence(int a[], int n)
{
// stores the index of elements
unordered_map mp;
// stores the length of the longest
// subsequence that ends with a[i]
int dp[n];
memset(dp, 0, sizeof(dp));
int maximum = INT_MIN;
// iterate for all element
for (int i = 0; i < n; i++) {
// if a[i]-1 is present before i-th index
if (mp.find(a[i] - 1) != mp.end()) {
// last index of a[i]-1
int lastIndex = mp[a[i] - 1] - 1;
// relation
dp[i] = 1 + dp[lastIndex];
}
else
dp[i] = 1;
// stores the index as 1-index as we need to
// check for occurrence, hence 0-th index
// will not be possible to check
mp[a[i]] = i + 1;
// stores the longest length
maximum = max(maximum, dp[i]);
}
return maximum;
}
// Driver Code
int main()
{
int a[] = { 3, 10, 3, 11, 4, 5, 6, 7, 8, 12 };
int n = sizeof(a) / sizeof(a[0]);
cout << longestSubsequence(a, n);
return 0;
} Java
// Java program to find length of the
// longest increasing subsequence
// whose adjacent element differ by 1
import java.util.*;
class lics {
static int LongIncrConseqSubseq(int arr[], int n)
{
// create hashmap to save latest consequent
// number as "key" and its length as "value"
HashMap map = new HashMap<>();
// put first element as "key" and its length as "value"
map.put(arr[0], 1);
for (int i = 1; i < n; i++) {
// check if last consequent of arr[i] exist or not
if (map.containsKey(arr[i] - 1)) {
// put the updated consequent number
// and increment its value(length)
map.put(arr[i], map.get(arr[i] - 1) + 1);
// remove the last consequent number
map.remove(arr[i] - 1);
}
// if their is no last consequent of
// arr[i] then put arr[i]
else {
map.put(arr[i], 1);
}
}
return Collections.max(map.values());
}
// driver code
public static void main(String args[])
{
// Take input from user
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int arr[] = new int[n];
for (int i = 0; i < n; i++)
arr[i] = sc.nextInt();
System.out.println(LongIncrConseqSubseq(arr, n));
}
}
// This code is contributed by CrappyDoctor Python3
# python program to find length of the
# longest increasing subsequence
# whose adjacent element differ by 1
from collections import defaultdict
import sys
# function that returns the length of the
# longest increasing subsequence
# whose adjacent element differ by 1
def longestSubsequence(a, n):
mp = defaultdict(lambda:0)
# stores the length of the longest
# subsequence that ends with a[i]
dp = [0 for i in range(n)]
maximum = -sys.maxsize
# iterate for all element
for i in range(n):
# if a[i]-1 is present before i-th index
if a[i] - 1 in mp:
# last index of a[i]-1
lastIndex = mp[a[i] - 1] - 1
# relation
dp[i] = 1 + dp[lastIndex]
else:
dp[i] = 1
# stores the index as 1-index as we need to
# check for occurrence, hence 0-th index
# will not be possible to check
mp[a[i]] = i + 1
# stores the longest length
maximum = max(maximum, dp[i])
return maximum
# Driver Code
a = [3, 10, 3, 11, 4, 5, 6, 7, 8, 12]
n = len(a)
print(longestSubsequence(a, n))
# This code is contributed by Shrikant13C#
// C# program to find length of the
// longest increasing subsequence
// whose adjacent element differ by 1
using System;
using System.Collections.Generic;
class GFG{
static int longIncrConseqSubseq(int []arr,
int n)
{
// Create hashmap to save
// latest consequent number
// as "key" and its length
// as "value"
Dictionary map = new Dictionary();
// Put first element as "key"
// and its length as "value"
map.Add(arr[0], 1);
for (int i = 1; i < n; i++)
{
// Check if last consequent
// of arr[i] exist or not
if (map.ContainsKey(arr[i] - 1))
{
// put the updated consequent number
// and increment its value(length)
map.Add(arr[i], map[arr[i] - 1] + 1);
// Remove the last consequent number
map.Remove(arr[i] - 1);
}
// If their is no last consequent of
// arr[i] then put arr[i]
else
{
if(!map.ContainsKey(arr[i]))
map.Add(arr[i], 1);
}
}
int max = int.MinValue;
foreach(KeyValuePair entry in map)
{
if(entry.Value > max)
{
max = entry.Value;
}
}
return max;
}
// Driver code
public static void Main(String []args)
{
// Take input from user
int []arr = {3, 10, 3, 11,
4, 5, 6, 7, 8, 12};
int n = arr.Length;
Console.WriteLine(longIncrConseqSubseq(arr, n));
}
}
// This code is contributed by gauravrajput1 输出：
6
时间复杂度： O(n)
辅助空间： O(n)