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// 736. Parse Lisp Expression
#include "leetcode.h"
struct var {
int val;
int name_size;
char *name;
struct var *next;
};
struct scope {
struct var *head;
struct scope *up;
};
static struct var *scope_local_lookup(struct scope *s, char *var_name,
int name_size) {
for (struct var *n = s->head; n; n = n->next) {
int cmp_size = n->name_size;
cmp_size = cmp_size < name_size ? name_size : cmp_size;
if (!strncmp(var_name, n->name, cmp_size))
return n;
}
return NULL;
}
static struct var *scope_local_define(struct scope *s, char *var_name,
int name_size) {
struct var **n;
int cmp_size;
for (n = &s->head; *n; n = &(*n)->next) {
cmp_size = (*n)->name_size;
cmp_size = cmp_size < name_size ? name_size : cmp_size;
if (!strncmp(var_name, (*n)->name, cmp_size))
return *n;
}
*n = (struct var *)malloc(sizeof(struct var));
if (!(*n))
return NULL;
(*n)->name = var_name;
(*n)->name_size = name_size;
(*n)->next = NULL;
return *n;
}
static struct var *scope_global_lookup(struct scope *s, char *var_name,
int name_size) {
for (struct scope *n = s; n; n = n->up) {
struct var *v = scope_local_lookup(n, var_name, name_size);
if (v)
return v;
}
return NULL;
}
static void scope_free_data(struct scope *s) {
for (struct var *n = s->head, *t; n;) {
t = n;
n = n->next;
free(t);
}
s->head = NULL;
}
static void scope_free(struct scope *s) {
for (struct scope *n = s, *t; n;) {
t = n;
n = n->up;
scope_free_data(t);
free(t);
}
}
static struct scope *push_scope(struct scope **s) {
struct scope *parent = *s;
*s = (struct scope *)malloc(sizeof(struct scope));
if (!(*s)) {
*s = parent;
return NULL;
}
(*s)->up = parent;
(*s)->head = NULL;
return *s;
}
static struct scope *pop_scope(struct scope **s) {
struct scope *parent = (*s)->up;
scope_free_data(*s);
free(*s);
return *s = parent;
}
enum token_state { END, INT, NAME, SEXP, CLOSE };
struct token {
int type;
int len;
int val;
char *str;
};
static int token_next(char **s, struct token *dst) {
int status = 1, sign;
for (; isspace(**s); ++(*s))
;
if (**s == '\0') {
dst->len = 0;
dst->type = END;
return 1;
}
dst->str = *s;
if (isdigit(**s) || **s == '-' || **s == '+') {
sign = **s == '-';
if (**s == '-' || **s == '+')
++(*s);
dst->type = INT;
dst->val = 0;
for (; isdigit(**s); ++(*s))
dst->val = dst->val * 10 - (**s - '0');
dst->val = sign ? dst->val : -dst->val;
} else if (isalpha(**s)) {
dst->type = NAME;
for (; isalnum(**s); ++(*s))
;
} else if (**s == '(') {
dst->type = SEXP;
++(*s);
} else if (**s == ')') {
status = 0;
dst->type = CLOSE;
++(*s);
}
dst->len = *s - dst->str;
return status;
}
static int eval(char **s, int *res, struct token *t, struct scope **curr);
static int evaluate_command_let(char **s, int *res, struct token *t,
struct scope **curr) {
struct var *v;
char *old_pos, *var_name;
int var_name_size, var_val;
if (!push_scope(curr))
return 0;
for (;;) {
old_pos = *s;
if (!token_next(s, t))
return 0;
if (t->type == NAME) {
var_name = t->str;
var_name_size = t->len;
if (!eval(s, &var_val, t, curr)) {
*s = old_pos;
break;
}
v = scope_local_define(*curr, var_name, var_name_size);
if (!v)
return 0;
v->val = var_val;
} else {
*s = old_pos;
break;
}
}
if (!eval(s, res, t, curr))
return 0;
if (token_next(s, t))
return 0;
pop_scope(curr);
return 1;
}
static int evaluate_command_add(char **s, int *res, struct token *t,
struct scope **curr) {
int op1, op2;
if (!eval(s, &op1, t, curr))
return 0;
if (!eval(s, &op2, t, curr))
return 0;
*res = op1 + op2;
if (token_next(s, t))
return 0;
return 1;
}
static int evaluate_command_mult(char **s, int *res, struct token *t,
struct scope **curr) {
int op1, op2;
if (!eval(s, &op1, t, curr))
return 0;
if (!eval(s, &op2, t, curr))
return 0;
*res = op1 * op2;
if (token_next(s, t))
return 0;
return 1;
}
static int evaluate_command(char **s, int *res, struct token *t,
struct scope **curr) {
char *cmd = t->str;
int cmd_size = t->len;
if (!strncmp(cmd, "let", cmd_size))
return evaluate_command_let(s, res, t, curr);
if (!strncmp(cmd, "add", cmd_size))
return evaluate_command_add(s, res, t, curr);
if (!strncmp(cmd, "mult", cmd_size))
return evaluate_command_mult(s, res, t, curr);
}
static int evaluate_sexp(char **s, int *res, struct token *t,
struct scope **curr) {
if (!token_next(s, t))
return 0;
if (t->type == NAME)
return evaluate_command(s, res, t, curr);
return 0;
}
static int eval(char **s, int *res, struct token *t, struct scope **curr) {
struct var *v;
if (!token_next(s, t))
return 0;
switch (t->type) {
case END:
*res = 0;
return 1;
case SEXP:
return evaluate_sexp(s, res, t, curr);
case INT:
*res = t->val;
return 1;
case NAME:
v = scope_global_lookup(*curr, t->str, t->len);
if (!v)
return 0;
*res = v->val;
return 1;
default:
return 0;
}
}
int evaluate(char *expression) {
struct scope *curr = NULL;
struct token t;
char *s = expression;
int ans = 0;
if (!eval(&s, &ans, &t, &curr)) {
scope_free(curr);
return -1;
}
return ans;
}
int main() {
char *e1 = "(let x 2 (mult x (let x 3 y 4 (add x y))))";
char *e2 = "let x 3 x 2 x)";
char *e3 = "(let x 1 y 2 x (add x y) (add x y))";
printf("%d\n", evaluate(e1)); // expect: 14
printf("%d\n", evaluate(e2)); // expect: 2
printf("%d\n", evaluate(e3)); // expect: 5
}
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