Swim in Rising Water

def swimInWater(grid):
    N = len(grid)
    visit = set()
    minH = [[grid[0][0], 0, 0]] # (time/max-height, r, c)
    directions = [[0, 1], [0, -1], [1, 0], [-1, 0]]
    visit.add((0, 0))
    
    while minH:
        t, r, c = heapq.heappop(minH)
        if r == N - 1 and c == N - 1:
            return t
        for dr, dc in directions:
            neiR, neiC = r + dr, c + dc
            if (neiR < 0 or neiR == N or 
                neiC < 0 or neiC == N or 
                (neiR, neiC) in visit):
                continue
            visit.add((neiR, neiC))
            heapq.heappush(minH, [max(t, grid[neiR][neiC]), neiR, neiC])