Pacific Atlantic Water Flow

def pacificAtlantic(heights):
    ROWS, COLS = len(heights), len(heights[0])
    pac, atl = set(), set()
    
    def dfs(r, c, visit, prevHeight):
        if ((r, c) in visit or r < 0 or c < 0 or 
            r == ROWS or c == COLS or heights[r][c] < prevHeight):
            return
        visit.add((r, c))
        dfs(r + 1, c, visit, heights[r][c])
        dfs(r - 1, c, visit, heights[r][c])
        dfs(r, c + 1, visit, heights[r][c])
        dfs(r, c - 1, visit, heights[r][c])
        
    for c in range(COLS):
        dfs(0, c, pac, heights[0][c])
        dfs(ROWS - 1, c, atl, heights[ROWS - 1][c])
        
    for r in range(ROWS):
        dfs(r, 0, pac, heights[r][0])
        dfs(r, COLS - 1, atl, heights[r][COLS - 1])
        
    res = []
    for r in range(ROWS):
        for c in range(COLS):
            if (r, c) in pac and (r, c) in atl:
                res.append([r, c])
    return res