well.c

#include <stdio.h>
#include <unistd.h>

#define MAX 256

void
print(int *grid, int w, int h, int t, int s, int d)
{
    fputs("\x1b[H",stdout); // cursor to "home"
    printf("t = %ds\n", t);
    for (int y = 0; y < h; y++) {
        for (int x = 0; x < w; x++) {
            int i = y * w + x;
            if (i == s)
                fputs("\x1b[93;1m",stdout);
            else if (i == d)
                fputs("\x1b[94;1m",stdout);
            printf("%-5.1f", grid[i] / (float)(w * h));
            if (i == s || i == d)
                fputs("\x1b[0m",stdout);
        }
        putchar('\n');
    }
}

static void
fill(int *grid, int w, int h, int i, char *visited)
{
    static const int d[] = {
        +1, +0, -1, +0, +0, +1, +0, -1, +1, +1, +1, -1, -1, +1, -1, -1,
    };
    int x = i % w;
    int y = i / w;
    visited[i] = 1;
    grid[i]++;
    for (int j = 0; j < 8; j++) {
        int tx = x + d[j * 2 + 0];
        int ty = y + d[j * 2 + 1];
        int ti = ty * w + tx;
        if (tx >= 0 && tx < w && ty >= 0 && ty < h && !visited[ti]) {
            if (grid[i] > grid[ti]) {
                grid[i]--;
                fill(grid, w, h, ti, visited);
                break;
            }
        }
    }
}

int
main(void)
{
    int w, h, dst;
    int grid[MAX];
    scanf("%d%d", &w, &h);
    for (int i = 0; i < w * h; i++)
        scanf("%d", grid + i);
    scanf("%d", &dst);

    int soff = 0;
    int doff = 0;
    int dval = (dst + 1) * w * h;
    for (int i = 0; i < w * h; i++) {
        if (grid[i] == 1)
            soff = i;
        if (grid[i] == dst)
            doff = i;
        grid[i] *= w * h;
    }

    int t = 0;
    fputs("\e[2J",stdout); // clear terminal
    print(grid,w,h,0,soff,doff);usleep(250000);
    for (; grid[doff] < dval; t++) {
        for (int i = 0; i < w * h; i++) {
            char visited[MAX] = {0};
            fill(grid, w, h, soff, visited);
        }
        print(grid,w,h,t+1,soff,doff);
        usleep(250000);
    }
    printf("%d\n", t);
}