Consistent monotonic subsequence - c++

Question

I have problem with this algorithm. It should search for longest consistent and monotonic subsequence and sum of it. If there are few subsequense with the same length it should return the first one.
It should work as monotonic function - http://en.wikipedia.org/wiki/Monotonic_function
For input : 1 1 7 3 2 0 0 4 5 5 6 2 1
the result is : 6 20 - so it works.
But for input : 23 34 11 5 23 90 11 10 15 12 28 49
the result is : 3 113 - but should be 3 50
I feel that the problem is in switching between increasing and decreasing case. Any idea?
code :
#include <stdio.h>
#define gc getchar
void scan_integer(unsigned long long int* o)
{
register unsigned long long int c = gc();
int x = 0;
for (; ((c<48 || c>57)); c = gc());
for (; c>47 && c<58; c = gc()) {
x = (x << 1) + (x << 3) + c - 48;
}
*o = x;
}
int main(){
unsigned long long int current_value, last_value, sum_increasing, sum_decreasing, length_increasing, length_decreasing, max_length, max_sum, is_increasing;
bool equal = false;
scan_integer(&current_value);
last_value = 0;
sum_increasing = current_value;
sum_decreasing = current_value;
length_increasing = 1;
length_decreasing = 1;
max_length = 1;
max_sum = current_value;
is_increasing = 0;
while (!feof(stdin))
{
last_value = current_value;
scan_integer(&current_value);
if (current_value == last_value){
sum_increasing += current_value;
sum_decreasing += current_value;
length_increasing += 1;
length_decreasing += 1;
equal = true;
}
else {
if (current_value > last_value){
sum_increasing += current_value;
length_increasing += 1;
if (equal == true){
length_decreasing = 1;
sum_decreasing = 0;
equal = false;
}
if (is_increasing < 0){
sum_increasing += last_value;
if (length_decreasing > max_length){
max_length = length_decreasing;
max_sum = sum_decreasing;
}
sum_decreasing = 0;
length_decreasing = 1;
}
is_increasing = 1;
}
else {
sum_decreasing += current_value;
length_decreasing += 1;
if (equal == true){
length_increasing = 1;
sum_increasing = 0;
equal = false;
}
if (is_increasing == 1){
sum_decreasing += last_value;
if (length_increasing > max_length){
max_length = length_increasing;
max_sum = sum_increasing;
}
sum_increasing = 0;
length_increasing = 1;
}
is_increasing = -1;
}
}
}
printf("%llu %llu", max_length, max_sum);
return 0;
}

Answer 1

I see a problem in the code, in this part:
is_increasing = 1; // here
// Did you mean to write a continue here?
}
else {
sum_decreasing += current_value;
length_decreasing += 1;
if (equal == true){
length_increasing = 1;
sum_increasing = 0;
equal = false;
}
if (is_increasing == 1){
sum_decreasing += last_value;
if (length_increasing > max_length){
max_length = length_increasing;
max_sum = sum_increasing;
}
sum_increasing = 0;
length_increasing = 1;
}
is_increasing = -1; // Or you might want to put this inside of the else above
If I understand correctly, 'is_increasing = -1' at the bottom completely invalidates the setting of it in the true condition of the if statemen (at the top of the code above). That's why, In the "else" that handles decreasing sequences 'is_increasing' always has the value of '-1' and such sequences never get saved as good sequences.
I put some codes in the code I copied and pasted. I think that handling the codition at which two numbers in sequence might need a little more care than those comments, but this should set you in the right direction.
Let me know if this helps.