Longest Increasing and Decreasing Subsequence program added under DP …

…Directory

DP/longest_increasing_and_decreasing_subsequence.cpp

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+/*
+Given an unsorted array on integers, find the length of its largest sub-sequence 
+such that it is increasing at first and then decreasing and the number of elements 
+in increasing and decreasing parts should be the same.
+
+Example:
+Input: 1 2 3 2 1 4 5 6 7 19 15 12 10 9
+Output: 9
+Explanation: Longest Increasing and Decreasing Sequence is:
+				1 4 5 6 7 19 15 12 10 9 ==> 9 elements
+
+*/
+
+
+#include<iostream> 
+#include <vector> 
+#include <bits/stdc++.h>
+using namespace std;
+int min(int a,int b)
+{
+	if(a<b)
+		return a;
+	return b;
+}
+int max(int a,int b)
+{
+	if(a>b)
+		return a;
+	return b;
+}
+int main()
+{
+	int n,tmp,inc,dec;
+	cin>>n;
+	vector<int> ip;
+	for(int i=0;i<n;i++)
+	{
+		cin>>tmp;
+		ip.push_back(tmp);
+	}
+	vector<int> lis(n,1);
+	vector<int> lds(n,1);
+	inc=0;
+	dec=0;
+	for(int i=1;i<n;i++)
+	{
+		if(ip[i]>ip[i-1])
+		{
+			lis[i]=lis[i]+(++inc);
+		}
+		else
+		{
+			inc=0;
+		}
+	}
+//	cout<<ip[n-1]<<"\t"<<lis[n-1]<<"\t"<<lds[n-1]<<lis[n-1]+lds[n-1]-1<<endl;
+	for(int i=n-2;i>=0;i--)
+	{
+
+		if(ip[i]>ip[i+1])
+		{
+			lds[i]=lds[i]+(++dec);
+		}
+		else
+		{
+			dec=0;
+		}
+//		cout<<ip[i]<<"\t"<<lis[i]<<"\t"<<lds[i]<<"\t"<<lis[i]+lds[i]-1<<endl;
+	}
+	int mx= INT_MIN;
+	for(int i=0;i<n;i++)
+	{
+//		cout<<2*min(lis[i],lds[i])-1<<endl;
+		mx=max(2*min(lis[i],lds[i])-1,mx);
+	}
+	cout<<mx;
+}