Last active
May 15, 2016 19:35
-
-
Save diogommartins/d5705013de144b63c67853ee918e8a22 to your computer and use it in GitHub Desktop.
Optimal Binary Search Tree
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
import sys | |
from pandas import DataFrame | |
def optimal_bst(keys, frequencies): | |
n = len(keys) | |
cost = [[0 for j in range(n)] for i in range(n)] # Cria matriz com elementos = nulo | |
# Popula diagonal | |
for i in range(n): | |
cost[i][i] = frequencies[i] | |
for chain_length in range(2, n+1): | |
for i in range(n - chain_length + 1): | |
# Pega coluna j através da linha i e do tamanho da cadeia | |
j = i + chain_length - 1 | |
cost[i][j] = sys.maxsize | |
for r in range(j+1): | |
sub1 = cost[i][r-1] if r > i else 0 | |
sub2 = cost[r+1][j] if r < j else 0 | |
c = sub1 + sub2 + sum(frequencies[i:j+1]) | |
if c < cost[i][j]: | |
cost[i][j] = c | |
print(DataFrame(cost)) | |
return cost[0][n-1] | |
if __name__ == "__main__": | |
keys = [10, 12, 20] | |
frequencies = [34, 8, 50] | |
cost = optimal_bst(keys, frequencies) | |
assert cost == 142 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment