ronith
10/31/2018 - 5:53 AM

## Maximum sum such that no two elements are adjacent

Given an array of positive numbers, find the maximum sum of a subsequence with the constraint that no 2 numbers in the sequence should be adjacent in the array. So 3 2 7 10 should return 13 (sum of 3 and 10) or 3 2 5 10 7 should return 15 (sum of 3, 5 and 7).Answer the question in most efficient way.

Examples : Input : arr[] = {5, 5, 10, 100, 10, 5} Output : 110 Input : arr[] = {1, 2, 3} Output : 4 Input : arr[] = {1, 20, 3} Output : 20

Algorithm: Loop for all elements in arr[] and maintain two sums incl and excl where incl = Max sum including the previous element and excl = Max sum excluding the previous element. Max sum excluding the current element will be max(incl, excl) and max sum including the current element will be excl + current element (Note that only excl is considered because elements cannot be adjacent). At the end of the loop return max of incl and excl.

``````//https://www.geeksforgeeks.org/maximum-sum-such-that-no-two-elements-are-adjacent/
#include <iostream>
using namespace std;

int main() {
int n;
cin>>n;
int a[n];
for (int i=0;i<n;i++)
cin>> a[i];
int inc=a[0], exc=0, ex;

for (int i=1;i<n;i++) {
ex= (inc>exc)?inc:exc;

inc= exc + a[i];
exc= ex;
}
inc>exc?cout<<inc:cout<<exc;
}
``````