I have recently attended a programming test in codility, and the question is to find the Number of bounded slice in an array..
I am just giving you breif explanation of
Finally a code that works according to the below mentioned idea. This outputs 9. (The code is in C++. You can change it for Java)
#include
using namespace std;
int main()
{
int A[] = {3,5,6,7,3};
int K = 2;
int i = 0;
int j = 0;
int minValue = A[0];
int maxValue = A[0];
int minIndex = 0;
int maxIndex = 0;
int length = sizeof(A)/sizeof(int);
int count = 0;
bool stop = false;
int prevJ = 0;
while ( (i < length || j < length) && !stop ) {
if ( maxValue - minValue <= K ) {
if ( j < length-1 ) {
j++;
if ( A[j] > maxValue ) {
maxValue = A[j];
maxIndex = j;
}
if ( A[j] < minValue ) {
minValue = A[j];
minIndex = j;
}
} else {
count += j - i + 1;
stop = true;
}
} else {
if ( j > 0 ) {
int range = j - i;
int count1 = range * (range + 1) / 2; // Choose 2 from range with repitition.
int rangeRep = prevJ - i; // We have to subtract already counted ones.
int count2 = rangeRep * (rangeRep + 1) / 2;
count += count1 - count2;
prevJ = j;
}
if ( A[j] == minValue ) {
// first reach the first maxima
while ( A[i] - minValue <= K )
i++;
// then come down to correct level.
while ( A[i] - minValue > K )
i++;
maxValue = A[i];
} else {//if ( A[j] == maxValue ) {
while ( maxValue - A[i] <= K )
i++;
while ( maxValue - A[i] > K )
i++;
minValue = A[i];
}
}
}
cout << count << endl;
return 0;
}
Algorithm (minor tweaking done in code):
Keep two pointers i & j and maintain two values minValue and maxValue..
1. Initialize i = 0, j = 0, and minValue = maxValue = A[0];
2. If maxValue - minValue <= K,
- Increment count.
- Increment j.
- if new A[j] > maxValue, maxValue = A[j].
- if new A[j] < minValue, minValue = A[j].
3. If maxValue - minValue > K, this can only happen iif
- the new A[j] is either maxValue or minValue.
- Hence keep incrementing i untill abs(A[j] - A[i]) <= K.
- Then update the minValue and maxValue and proceed accordingly.
4. Goto step 2 if ( i < length-1 || j < length-1 )