Algorithm 2 Class engagement analysis (CEA) algorithm.

Input: A new LCC message $〈id,desc,time,loc〉$, hash table $H_T$, location q, time length T, small positive number $\epsilon$.

Output: Hash table $H_T$ with the engagement ratio r.

if $id$ is not a key in $H_T$ then

if $loc\in q$ AND $desc$ = LAS then

$T_{LAS}\leftarrow T$; $T_{LIS}\leftarrow \epsilon$;

else if $loc\in q$ AND $desc$ = LIS then

$T_{LAS}\leftarrow 0$; $T_{LIS}\leftarrow T$;

$r\leftarrow \frac{T_{LAS}}{T_{LIS}}$;

Insert a new key-value pair $(id,[q,r,T_{LIS}])$ into $H_T$;

else if $id$ is an existing key in $H_T$ then

Get the value $[q,r,T_{LIS}]$ from $H_T$ using $id$;

if $loc\in q$ AND $desc=LAS$ then

$r\leftarrow \frac{r\ast T_{LIS}+T}{T_{LIS}}$;

else if $loc\in q$ AND $desc=LIS$ then

$r\leftarrow \frac{r\ast T_{LIS}}{T_{LIS}+T}$; $T_{LIS}\leftarrow T_{LIS}+T$

Update the latest key-value pair $(id,[q,r,T_{LIS}])$ into $H_T$;