1 files changed, 111 insertions, 0 deletions
diff --git a/Advent-of-Code-2020/AOC-2/main.c b/Advent-of-Code-2020/AOC-2/main.c
new file mode 100644
index 0000000..72f8aa5
--- /dev/null
+++ b/Advent-of-Code-2020/AOC-2/main.c
@@ -0,0 +1,111 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#if 0
+  #define PFILE "sample.txt"
+#else
+  #define PFILE "input.txt"
+#endif
+
+size_t valid_passwds1;
+size_t valid_passwds2;
+
+void Parts()
+{
+  char ch;
+  FILE *fp;
+  fp = fopen(PFILE, "r");
+  if(fp == NULL) assert(0);
+
+  size_t passwd_cap = 100;
+  size_t tstr_cap = 4;
+  
+  int num1 = 0;
+  int num2 = 0;
+  char passwd_char;
+  char password[passwd_cap];  size_t passwd_sz = 0;
+  
+  char temp_str1[tstr_cap]; size_t i_tstr1 = 0;
+  char temp_str2[tstr_cap]; size_t i_tstr2 = 0;
+  char temp_str3[passwd_cap]; size_t i_tstr3 = 0;
+  
+  int mode = 0; // 0-read nums; 1-read num2; 2-read char; 3-read pass
+  while((ch = fgetc(fp)) != EOF)
+  {
+    // Parse
+    if(mode == 0)
+    {
+      if(ch == '-') { i_tstr1 = 0; mode = 1; continue; }
+      temp_str1[i_tstr1] = ch;
+      i_tstr1 += 1;
+      assert(i_tstr1 < tstr_cap);
+    }
+    else if(mode == 1)
+    {
+      if(ch == ' ') { i_tstr2 = 0; mode = 2; continue; }
+      temp_str2[i_tstr2] = ch;
+      i_tstr2 += 1;
+      assert(i_tstr2 < tstr_cap);
+    }
+    else if(mode == 2)
+    {
+      if(ch == ':') continue;
+      if(ch == ' ') { mode = 3; continue; };
+      passwd_char = ch;
+    }
+    else if(mode == 3)
+    {
+      if(ch != '\n')
+      {
+	temp_str3[i_tstr3] = ch;
+	i_tstr3 += 1;
+	assert(i_tstr3 < passwd_cap);
+      }
+      else
+      {
+	passwd_sz= i_tstr3;
+	i_tstr3 = 0;
+	mode = 0;
+      }
+    }
+
+    if(ch == '\n')
+    {
+      temp_str1[tstr_cap - 1] = '\0';
+      temp_str2[tstr_cap - 1] = '\0';
+      temp_str3[passwd_sz] = '\0';
+      num1 = atoi(temp_str1);
+      num2 = atoi(temp_str2);
+      strcpy(password, temp_str3);
+      
+      // reset all vars
+      memset(temp_str1, 0, sizeof(char)*tstr_cap);
+      memset(temp_str2, 0, sizeof(char)*tstr_cap);
+      memset(temp_str3, 0, sizeof(char)*passwd_cap);
+
+      // ## Part 1 ##
+      // check password validity
+      size_t seen_char = 0;
+      for(int i=0; i<passwd_sz; i++)
+	if(password[i] == passwd_char) seen_char += 1;     
+      if(seen_char >= num1 && seen_char <= num2) valid_passwds1 += 1;
+
+      // ## Part 2 ##
+      if(!(password[num1-1] == passwd_char) != !(password[num2-1] == passwd_char)) //XOR !a != !b
+	valid_passwds2 += 1;
+    }
+  }
+  
+  fclose(fp);
+
+  printf("RESULT-1: %d\n", valid_passwds1);
+  printf("RESULT-2: %d\n", valid_passwds2);
+}
+
+int main()
+{
+  Parts();
+  return 0;
+}