exercism.c

#include "matching_brackets.h"
#include <string.h>

struct Stack {
  int top;
  char data[20];
};

void push(struct Stack *s, char elem) {
  s->top++;
  s->data[s->top] = elem;
}

void pop(struct Stack *s) {
  s->top--;
}

char peek(struct Stack *s) { return s->data[s->top]; }

bool is_open(char c) { return c == '{' || c == '[' || c == '('; }

bool is_closed(char c) { return c == '}' || c == ']' || c == ')'; }

char opposing(char *c) {
  switch (*c) {
  case '}':
    return '{';

  case ')':
    return '(';

  case ']':
    return '[';

  default:
    return '\n';
  }
}

bool is_paired(const char *input) {
  struct Stack stack;
  size_t i;
  stack.top = -1;

  for (i = 0; i < strlen(input); i++) {
    char c = input[i];

    if (is_open(c)) {
      push(&stack, c);
    } else if (is_closed(c)) {
      if (peek(&stack) == opposing(&c)) {
        pop(&stack);
      } else {
        return false;
      }
    } else {
      // char we do not care about
    }
  }
  return stack.top == -1;
}