As we discussed in Set 1, following are the two main properties of a problem that suggest that the given problem can be solved using Dynamic programming:

1) Overlapping Subproblems

2) Optimal Substructure

We have already discussed Overlapping Subproblem property in the Set 1. Let us discuss Optimal Substructure property here.

** 2) Optimal Substructure: ** A given problems has Optimal Substructure Property if optimal solution of the given problem can be obtained by using optimal solutions of its subproblems.

For example, the Shortest Path problem has following optimal substructure property:

If a node x lies in the shortest path from a source node u to destination node v then the shortest path from u to v is combination of shortest path from u to x and shortest path from x to v. The standard All Pair Shortest Path algorithms like Floyd–Warshall and Bellman–Ford are typical examples of Dynamic Programming.

On the other hand, the Longest Path problem doesn’t have the Optimal Substructure property. Here by Longest Path we mean longest simple path (path without cycle) between two nodes. Consider the following unweighted graph given in the CLRS book. There are two longest paths from q to t: q→r→t and q→s→t. Unlike shortest paths, these longest paths do not have the optimal substructure property. For example, the longest path q→r→t is not a combination of longest path from q to r and longest path from r to t, because the longest path from q to r is q→s→t→r and the longest path from r to t is r→q→s→t.

We will be covering some example problems in future posts on Dynamic Programming.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

**References:**

http://en.wikipedia.org/wiki/Optimal_substructure

CLRS book

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the **DSA Self Paced Course** at a student-friendly price and become industry ready.

## Recommended Posts:

- Optimal Strategy for the Divisor game using Dynamic Programming
- Overlapping Subproblems Property in Dynamic Programming | DP-1
- Optimal Binary Search Tree | DP-24
- Optimal Strategy for a Game | DP-31
- Optimal Strategy for a Game | Set 2
- Optimal Strategy for a Game | Set 3
- Optimal strategy for a Game with modifications
- Travelling Salesman Problem | Set 1 (Naive and Dynamic Programming)
- Vertex Cover Problem | Set 2 (Dynamic Programming Solution for Tree)
- Bitmasking and Dynamic Programming | Set 1 (Count ways to assign unique cap to every person)
- Compute nCr % p | Set 1 (Introduction and Dynamic Programming Solution)
- Dynamic Programming | High-effort vs. Low-effort Tasks Problem
- Top 20 Dynamic Programming Interview Questions
- Dynamic Programming | Building Bridges
- Bitmasking and Dynamic Programming | Set-2 (TSP)
- Dynamic Programming on Trees | Set-1
- Dynamic Programming on Trees | Set 2
- Number of Unique BST with a given key | Dynamic Programming
- Dynamic Programming vs Divide-and-Conquer
- Maximum sum of nodes in Binary tree such that no two are adjacent | Dynamic Programming