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42S-CS107-Practice-Key

# 42S-CS107-Practice-Key - CS107 Spring 2007 Handout 42S June...

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CS107 Handout 42S Spring 2007 June 4, 2007 CS107 Final Exam Practice Problem Solutions Solution 1: Matchmaking /** * The primary assumption is that both boys and girls * are C vectors of dynamically allocated C strings, each * initialized as follows. * * vector boys, girls; * VectorNew(&boys, sizeof(char *), StringFree, 0); * VectorNew(&girls, sizeof(char *), StringFree, 0); * * generateAllCouples creates a new C vector of couples * and inserts one such record on behalf of every possible * mapping of boy to girl. The couples own their own strings, * so that none of the three vectors share any memory whatsoever. * Assume that CoupleFree is the VectorFreeFunction that disposes * of couple records embedded in a vector, and assume it just works. */ typedef struct { char *girl; char *boy; } couple; vector generateAllCouples(vector *boys, vector *girls) { vector couples; VectorNew(&couples, sizeof(couple), CoupleFree, 0); int i, j; couple item; for (int i = 0; i < VectorLength(boys); i++) { for (int j = 0; j < VectorLength(girls); j++) { item.boy = strdup(*(char **) VectorNth(boys, i)); item.girl = strdup(*(char **) VectorNth(girls, j)); VectorAppend(&couples, &item); } } return couples; } Solution 2: Extending the vector typedef struct { void *elems; // pointer to elemsize * alloclength bytes of memory int elemsize; // number of bytes dedicated to each client element int loglength; // number of elements the client is storing int alloclength; // number of elements we have space for VectorFreeFunction free; // applied to elements as they are removed } vector; typedef bool (*VectorSplitFunction)(const void *elemAddr); void VectorSplit(vector *original, vector *thoseThatPass, vector *thoseThatFail, VectorSplitFunction test)

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2 { int i; void *elem; VectorNew(thoseThatPass, original->elemsize, original->free, 0); VectorNew(thoseThatFail, original->elemsize, original->free, 0); for (i = 0; i < original->loglength; i++) { elem = VectorNth(original, i); VectorAppend((test(elem) ? thoseThatPass : thoseThatFail), elem); } original->loglength = 0; // leave memory there… } Solution 3: Spice Rack class spice { spice *& saffron(spice& salt); short sage(int cumin, spice rosemary) { cumin *= thyme[cumin - *(char *)thyme]; return ((spice *) &parsley)->saffron(rosemary)->parsley - &rosemary; } short thyme[4]; spice *parsley; }; // line 1 R1 = M[SP + 8]; // load old cumin R2 = M[SP + 4]; R3 =.1 M[R2]; // load first byte of this->thyme[0] R4 = R1 – R3; // compute index R5 = R4 * 2; // scale by sizeof(short) R6 = R2 + R5; // compute address of rhs R7 =.2 M[R6]; // compute rhs R8 = R1 * R7; // compute new cumin value M[SP + 8] = R8; // flush to space for cumin // line 2 R10 = M[SP + 4]; // load this (again) R11 = R10 + 8; R12 = SP + 12; // prepare address of rosemary (which gets passed by ref) SP = SP – 8; // make space for params M[SP] = R11; // set down address of receiving object
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42S-CS107-Practice-Key - CS107 Spring 2007 Handout 42S June...

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