If st . top ( ) is present in the set s
if ( s . find ( st . top ( ) ) != s . end ( ) ) { s . erase ( st . top ( ) ) ; st . top ( ) -> left = node ; st . pop ( ) ; } else { st . top ( ) -> right = node ; } } st . push ( node ) ; } while ( post [ p -- ] != in [ i ] && p >= 0 ) ; node = NULL ;