Quad Sum Is N

Write a function to determine if an array a$[]$ has four distinct elements whose sum is equal to

some specified value n$.$

bool quad$\_$sum$\_$is$\_$n$($int a$[],$ int len, int n$)$;

Returns true if a$[]$ has four distinct elements whose sum $==$ n$.$ Otherwise, returns false.

Examples:

Input: a$[]=\{1,2,3,4\},$ len $=4,$ n $=10$

Returns: true

Explanation: $10==1+2+3+4$

Input: a$[]=\{1\},$ len $=1,$ n $=1$

Returns: false

Input: a$[]=\{-1,0,-2,5,1,6,2\},$ len $=7,$ n $=0$

Returns: true

Explanation: $0==-1+-2+1+2$