Find the min diff by comparing difference of all possible pairs in given array
for ( $ i = 0 ; $ i < $ n - 1 ; $ i ++ ) for ( $ j = $ i + 1 ; $ j < $ n ; $ j ++ ) if ( abs ( $ arr [ $ i ] - $ arr [ $ j ] ) < $ diff ) $ diff = abs ( $ arr [ $ i ] - $ arr [ $ j ] ) ;