C++ Wrong answer in code chef - c++

Question

Problem: http://www.codechef.com/problems/LEBOMBS
I have tried every single test case that come to my mind. But it still gives a wrong answer. I don't know why.
Please point out if there's any error in my code. This is my code.
#include <iostream>
using namespace std;
int main() {
int t, i, total, n;
char a[1001];
cin >> t;
while (t--) {
i = 0;
cin >> n;
total = n;
cin >> a;
while (i < n) {
if (a[i] == '1') {
if (i == '0')
total -= 2;
else if (i == 1) {
if (a[i - 1] == '1')
total--;
else
total -= 3;
} else if (i > 1 && i < n - 1) {
if (a[i - 1] == '1')
total--;
else if (a[i - 2] == '1')
total -= 2;
else
total -= 3;
} else {
if (a[i - 1] == '1')
;
else if (a[i - 2] == '1')
total--;
else
total -= 2;
}
}
i++;
}
if (total < 0)
total = 0;
cout << total << "\n";
}
return 0;
}
P.S. If you see the code, there is a line that says "if(total<0)total=0;" that is for the case when the number of buildings is equal to 1 or 2, because that case gave the wrong answer for the code that I wrote, but after that it gives a wrong answer. Please help.
And is there any way about how do I think a test case that might be violating my code for future reference?

Answer 1

Your method is really complicated, and I'm not sure why it is that way:
bool bombs_nearby(char *bombs, int length, int index) {
if (length == 1)
return bombs[0] == '1';
if (index == 0)
return bombs[0] == '1' || bombs[1] == '1';
if (index == length - 1)
return bombs[length - 1] == '1' || bombs[length - 2] == '1';
return bombs[index - 1] == '1' || bombs[index] == '1' || bombs[index + 1] == '1';
}
int remaining_buildings(char *bombs, int length) {
int total = 0;
for (int i=0; i<length; ++i)
if (!bombs_nearby(bombs, length, i))
total++;
return total;
}
And the test case code would just be:
cin >> n >> a;
cout << remaining_buildings(a, n) << "\n";
Test Cases
Additionally, here's a test case that you fail:
1 49 0101100010101110000101111101101010011010001100111
The correct answer is 4, but you only claim 2 houses will survive.
Why does your code fail that test case?
So, I spent some time re-reading your code. And it's actually not that bad of a method. I think if there was a comment describing what you were trying to do, it would have been very clear how you were going about it.
Sadly though, all of your pain is due to a very small bug:
while (i < n) {
if (a[i] == '1') {
if (i == '0')
total -= 2;
Note that you test i == '0'. You meant to do i == 0. You should be testing that you are not at the zeroth index, not that i is the '0' character.