Why cycle behaves differently in just one iteration?

Question

I have this code:

gs = open("graph.txt", "r")

gp = gs.readline()
gp_splitIndex = gp.find(" ")
gp_nodeCount = int(gp[0:gp_splitIndex])
gp_edgeCount = int(gp[gp_splitIndex+1:-1])

matrix = [] # predecare the array
for i in range(0, gp_nodeCount):
    matrix.append([])
    for y in range(0, gp_nodeCount):
        matrix[i].append(0)

for i in range(0, gp_edgeCount-1):
    gp = gs.readline()
    gp_splitIndex = gp.find(" ") # get the index of space, dividing the 2 numbers on a row
    gp_from = int(gp[0:gp_splitIndex])
    gp_to = int(gp[gp_splitIndex+1:-1])
    matrix[gp_from][gp_to] = 1

print matrix

The file graph.txt contains this:

5 10
0 1
1 2
2 3
3 4
4 0
0 3
3 1
1 4
4 2
2 0

The first two number are telling me, that GRAPH has 5 nodes and 10 edges. The Following number pairs demonstrate the edges between nodes. For example "1 4" means an edge between node 1 and 4.

Problem is, the output should be this:

[[0, 1, 0, 1, 0], [0, 0, 1, 0, 1], [1, 0, 0, 1, 0], [0, 1, 0, 0, 1], [1, 0, 1, 0, 0]]

But instead of that, I get this:

[[0, 1, 0, 1, 0], [0, 0, 1, 0, 1], [0, 0, 0, 1, 0], [0, 1, 0, 0, 1], [1, 0, 1, 0, 0]]

Only one number is different and I can't understand why is this happening. The edge "3 1" is not present. Can someone explain, where is the problem?

Answer 1

Change for i in range(0, gp_edgeCount-1): to

for i in range(0, gp_edgeCount):

The range() function already does the "-1" operation. range(0,3) "==" [0,1,2]

And it is not the "3 1" edge that is missing, it is the "2 0" edge that is missing, and that is the last edge. The matrices start counting at 0.