initial
I tried solving the prefix sum question like how a human would solve it. It works but could be cleaner. But lets see code
import sys
input = sys.stdin.readline
n = int(input())
lst = list(map(int,input().split()))
ans = [0 for _ in range(n)]
ans[0] = lst[0]
for i in range(1,n):
ans[i] += lst[i]+ans[i-1]
m= int(input())
for _ in range(m):
a,b = map(int,input().split())
if a>1:
print(ans[b-1]-ans[a-2])
else:
print(ans[b-1])solution
a better way is to add a 0 at the front of prefix sum list. This way, we dont have to separate our logic via if else statements like my impl.
import sys
input = sys.stdin.readline
N = int(input())
arr = [0] + list(map(int, input().split()))
prefix = [0] * len(arr)
for i in range(1, len(arr)):
prefix[i] = prefix[i - 1] + arr[i]
M = int(input())
for _ in range(M):
s, e = map(int, input().split())
print(prefix[e] - prefix[s - 1])complexity
n time and space
