제가 생각할 수 있는 모든 예제들을 넣어서 확인해 보았을 때 결과가 정상적으로 나오고 있는데
정답 제출만 하면 오답이라고 나오네요 T.T

혹시 어떤 부분이 잘못 된건지 알 수 있을까요?

제가 생각하는 기본 알고리즘은 주석으로 적었습니다...

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#define MAX_ROWCOL 501
#define manual_input 0  // how to get the input
#define debug 0 

int test_case;
int width, hight;
char bact_table[MAX_ROWCOL][MAX_ROWCOL];
int IsChanged = 0;
int seconds = 0;
int read_input();
int check_around(int row, int col);
void init_data();

int main() {
    int result = 0;
    result = read_input();
    return result;  // no meaning
}

int read_input() {
    int result = 0, IsExtinct =1;
    FILE * fp;
    if (!manual_input) {
        fp = fopen("input.txt", "rt");
        if (fp == NULL)
            return 1;
    }
    if(manual_input)
        scanf("%d", &test_case);    // input number of test case
    else
        fscanf(fp, "%d", &test_case);
    for (int k = 0; k < test_case; k++) {
        if (!manual_input)
            fscanf(fp, "%d %d", &width, &hight);
        else
            scanf("%d %d", &width, &hight); // input W and H
        for (int i = 0; i < hight; i++) {
            if (!manual_input)
                fscanf(fp, "%s", &bact_table[i]);   // input bacterias
            else
                scanf("%s", &bact_table[i]);
        }
        if (debug) {// only for debug 
            for (int i = 0; i < hight; i++) {
                for (int j = 0; j < width; j++) {
                    printf("%c", bact_table[i][j]);
                }
                printf("\n");
            }
        }
        while (1) {     // repeat until there are no change(dead)
            IsChanged = 0;
            IsExtinct = 1;
            for (int i = 0; i < hight; i++) {
                for (int j = 0; j < width; j++) {
                    result = check_around(i, j);
                    if (result)
                        IsExtinct = 0;  
                    // IsExtinct is a flag to check initial state have bacteria or not
                    if (debug) printf("%d", result);
                }
                if (debug) printf("\n");
            }

            for (int i = 0; i < hight; i++) {
                for (int j = 0; j < width; j++) {
                    if (bact_table[i][j] == '@') {  
                        // if bacteria died just ago, replace @ to . again.
                        bact_table[i][j] = '.';     
                        // and set IsChanged flag as true
                        IsChanged = 1;
                    }
                }
            }
            if (debug) printf("IsChanged : %d, seconds %d ,IsExtinct %d\n", IsChanged, seconds, IsExtinct);
            if (!IsChanged)     
                // stop if there are no change of bacteria life
                break;
            else
                // increase seconds counter if there are changes of bacteria life
                seconds++;      
                
        };
        // In case of all bacteria extincted or initial state have no bacteria
        if ((seconds && IsExtinct) || (!seconds && IsExtinct))  
            printf("%d\n", seconds);    // print seconds( or 0)
        else
            printf("-1\n");             // In case of no baceria extincts
        init_data();                    // init variables
    }
    if (!manual_input)
        fclose(fp);
    return 0;
}

int check_around(int row, int col) {
    int cnt =0, ret = 0;
    if (bact_table[row][col] == '*') {
        if (col)
            if ((bact_table[row][col - 1] == '*') 
                || (bact_table[row][col - 1] == '@')) // check left cell
                cnt++;
        if (col != (width - 1))
            if ((bact_table[row][col + 1] == '*') 
                || (bact_table[row][col + 1] == '@')) // check right cell
                cnt++;
        if (row)
            if ((bact_table[row - 1][col] == '*') 
                || (bact_table[row - 1][col] == '@')) // check upper cell
                cnt++;
        if (row != (hight -1))
            if ((bact_table[row + 1][col] == '*') 
                || (bact_table[row + 1][col] == '@')) //check below cell
                cnt++;
        ret = 1;
    }
    if ((cnt != 2) && (bact_table[row][col] != '.')) {  // if it will die
        bact_table[row][col] = '@';     // @ means just ago "dead" 
    }

    return ret;     // return 0 if it is not a bacteria
                    // return 1 if it is a bacteria
}

void init_data() {
    for (int i = 0; i < MAX_ROWCOL; i++)
        for (int j = 0; j < MAX_ROWCOL; j++) {
            bact_table[i][j] = 0;
        }
    IsChanged = 0;
    seconds = 0;

}