Rating:
# UMDCTF2021 - Jay 1
- Write-Up Author: Wendy \[[MOCTF](https://www.facebook.com/MOCSCTF)\]
- Flag:UMDCTF-{K4d4n35_41g0r1thm}
## **Question:**
Jay 1
## Write up
First, we run the program and identify the [Kadane’s algorithm](https://www.geeksforgeeks.org/largest-sum-contiguous-subarray/) from the program description. Given an array and calculate the Maximum contiguous sum.
Since we need to finish the calculation within 5 seconds, we have to write script to do it. Here we use pwn library for getting output and sending input from netcat.
```
from pwn import *
from sys import maxsize
def maxSubArraySum(a,size):
max_so_far = -maxsize - 1
max_ending_here = 0
start = 0
end = 0
s = 0
for i in range(0,size):
max_ending_here += int(a[i])
if max_so_far < max_ending_here:
max_so_far = max_ending_here
start = s
end = i
if max_ending_here < 0:
max_ending_here = 0
s = i+1
with open('result.txt', 'w') as f:
f.write("%d"%(max_so_far))
f.write(", ")
f.write("%d"%(start))
f.write(", ")
f.write("%d"%(end))
conn = remote('chals3.umdctf.io',6001,level='error')
print conn.recvuntil("Press Enter to get the arr")
conn.sendline("")
#print conn.recvuntil("]")
array = conn.recvuntil("]")
array2 = array[3:-1]
a = array2.split(', ')
print a
MaxCSum = maxSubArraySum(a,len(a))
file1 = open('result.txt', 'r')
MaxCSum = file1.read()
print MaxCSum
conn.sendline(MaxCSum)
print conn.recvuntil("}")
```
Finally, we got the flag!
>UMDCTF-{K4d4n35_41g0r1thm}
