solved day 4 part 2 in reasonable runtime

4_2/Makefile

@@ -0,0 +1,13 @@
+client: main.c
+	gcc -o main main.c -O3 -Wall -Wextra -g -march=x86-64-v3
+
+client-debug: main.c
+	gcc -o main main.c -O1 -Wall -Wextra -g -fsanitize=address
+
+client-debug-nosanitize: main.c
+	gcc -o main main.c -O1 -Wall -Wextra -g
+
+clean:
+	rm main
+
+.PHONY: clean

4_2/main.c

@@ -0,0 +1,141 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <time.h>
+
+char input[] =
+{
+#embed "input.txt"
+,'\0' // null terminator
+,'\0'
+};
+
+int width = 0;
+int height = 0;
+
+uint64_t power(uint64_t base, uint64_t exp) {
+    uint64_t i, result = 1;
+    for (i = 0; i < exp; i++)
+        result *= base;
+    return result;
+}
+
+
+void print_field(uint8_t* surrounds){
+    for(int x = 0; x < height; x++){
+        for(int y = 0; y < width; y++){
+            if(/*surrounds[(x)*(width+2)+(y)] < 4 &&*/ input[(x)*(width+1)+(y)] == '@'){
+                printf("%d", surrounds[(x)*(width+2)+(y)]);
+            }else{
+                printf("%c", input[(x)*(width+1)+(y)]);
+            }
+        }
+        printf("\n");
+    }
+}
+
+int main(int argc, char *argv[]){
+    clock_t start, end;
+    start = clock();
+
+    while(input[width] != '\n'){
+        width++;
+    }
+    //printf("width: %d\n", width);
+    
+    while(input[height*(width+1)+1] != 0){
+        height++;
+    }
+    //printf("height: %d\n", height);
+    
+
+    uint8_t* surrounds = calloc((height+2)*(width+2), sizeof(uint8_t))+width+1;
+
+    for(int x = 0; x < height; x++){
+        for(int y = 0; y< width; y++){
+            if(input[(x)*(width+1)+(y)] == '@'){
+                    surrounds[(x-1)*(width+2)+(y-1)]    += 1;
+                    surrounds[(x-1)*(width+2)+(y)]      += 1;
+                    surrounds[(x-1)*(width+2)+(y+1)]    += 1;
+                    surrounds[(x)*(width+2)+(y-1)]      += 1;
+                    surrounds[(x)*(width+2)+(y)]        += 0;
+                    surrounds[(x)*(width+2)+(y+1)]      += 1;
+                    surrounds[(x+1)*(width+2)+(y-1)]    += 1;
+                    surrounds[(x+1)*(width+2)+(y)]      += 1;
+                    surrounds[(x+1)*(width+2)+(y+1)]    += 1;
+            }
+            //if(surrounds[(x)*width+(y)] < 8 && input[(x)*(width+1)+(y)] == '@'){
+            //    printf("%d", surrounds[(x)*(width+2)+(y)]);
+            //}else{
+            //    printf("%c", input[(x)*(width+1)+(y)]);
+            //}
+        }
+        //printf("\n");
+    }
+    
+    uint64_t count = 0;
+    uint64_t count_2 = 0;
+    bool cont = true;
+    while (cont){
+        count_2 = 0;
+        for(int x = 0; x < height; x++){
+            for(int y = 0; y < width; y++){
+                if(surrounds[(x)*(width+2)+(y)] < 4 && input[(x)*(width+1)+(y)] == '@'){
+                    count_2++;
+                    input[(x)*(width+1)+(y)] = 'x';
+                    //printf("%d", surrounds[(x)*width+(y)]);
+                }else{
+                    //printf("%c", input[(x)*width+(y)]);
+                }
+            }
+            //printf("\n");
+        }
+        //print_field(surrounds);
+        count += count_2;
+        if(count_2 == 0){
+            cont = false;
+        }
+        //printf("cont: %s\n", cont ? "true" : "false");
+        //printf("count_2 = %lu\n", count_2);
+        //printf("count = %lu\n", count);
+        for(int x = 0; x < height; x++){
+            for(int y = 0; y < width; y++){
+                if(input[(x)*(width+1)+(y)] == 'x'){
+                    surrounds[(x-1)*(width+2)+(y-1)]    -= 1;
+                    surrounds[(x-1)*(width+2)+(y)]      -= 1;
+                    surrounds[(x-1)*(width+2)+(y+1)]    -= 1;
+                    surrounds[(x)*(width+2)+(y-1)]      -= 1;
+                    surrounds[(x)*(width+2)+(y)]        -= 0;
+                    surrounds[(x)*(width+2)+(y+1)]      -= 1;
+                    surrounds[(x+1)*(width+2)+(y-1)]    -= 1;
+                    surrounds[(x+1)*(width+2)+(y)]      -= 1;
+                    surrounds[(x+1)*(width+2)+(y+1)]    -= 1;
+                    input[(x)*(width+1)+(y)] = '.';
+                    //printf("%d", surrounds[(x)*width+(y)]);
+                }else{
+                    //printf("%c", input[(x)*width+(y)]);
+                }
+            }
+            //printf("\n");
+        }
+        //print_field(surrounds);
+        //sleep(1);
+    }
+
+
+    free(surrounds-width-1);
+
+    end = clock();
+    printf("count: %lu\n", count);
+    clock_t ticks_taken = end - start; 
+    double time_taken = ((double)ticks_taken)/CLOCKS_PER_SEC;
+    printf("time take: %f ticks\n", time_taken);
+    printf("CLOCKS_PER_SEC: %ld\n", CLOCKS_PER_SEC);
+
+
+    exit(1);
+}