If an internal node and is greater than its children , and same is recursively true for the children
if ( $ arr [ $ i ] >= $ arr [ 2 * $ i + 1 ] && $ arr [ $ i ] >= $ arr [ 2 * $ i + 2 ] && isHeap ( $ arr , 2 * $ i + 1 , $ n ) && isHeap ( $ arr , 2 * $ i + 2 , $ n ) ) return true ; return false ; }