Python/dynamic_programming/max_sub_array.py
2017-10-25 01:37:11 +05:30

60 lines
1.8 KiB
Python

"""
author : Mayank Kumar Jha (mk9440)
"""
import time
import matplotlib.pyplot as plt
from random import randint
def find_max_sub_array(A,low,high):
if low==high:
return low,high,A[low]
else :
mid=(low+high)//2
left_low,left_high,left_sum=find_max_sub_array(A,low,mid)
right_low,right_high,right_sum=find_max_sub_array(A,mid+1,high)
cross_left,cross_right,cross_sum=find_max_cross_sum(A,low,mid,high)
if left_sum>=right_sum and left_sum>=cross_sum:
return left_low,left_high,left_sum
elif right_sum>=left_sum and right_sum>=cross_sum :
return right_low,right_high,right_sum
else:
return cross_left,cross_right,cross_sum
def find_max_cross_sum(A,low,mid,high):
left_sum,max_left=-999999999,-1
right_sum,max_right=-999999999,-1
summ=0
for i in range(mid,low-1,-1):
summ+=A[i]
if summ > left_sum:
left_sum=summ
max_left=i
summ=0
for i in range(mid+1,high+1):
summ+=A[i]
if summ > right_sum:
right_sum=summ
max_right=i
return max_left,max_right,(left_sum+right_sum)
if __name__=='__main__':
inputs=[10,100,1000,10000,50000,100000,200000,300000,400000,500000]
tim=[]
for i in inputs:
li=[randint(1,i) for j in range(i)]
strt=time.time()
(find_max_sub_array(li,0,len(li)-1))
end=time.time()
tim.append(end-strt)
print("No of Inputs Time Taken")
for i in range(len(inputs)):
print(inputs[i],'\t\t',tim[i])
plt.plot(inputs,tim)
plt.xlabel("Number of Inputs");plt.ylabel("Time taken in seconds ")
plt.show()