% TeX root = ../main.tex

\begin{tikzpicture}[scale=0.5]
    \begin{axis}[
        axis lines = center,
        axis on top,
        xmin=-3.3,
        xmax=3.3,
        ymin=0,
        ymax=5.3,
        y=1cm,
        x=1cm,
        ytick={-0,...,5},
        xtick={-3,...,3},
        xlabel = x,
        ylabel = y,
        font=\tiny
    ]
        \addplot [ name path = A, thick ] {x + 4};
        \addplot [ name path = B, thick ] {x + 1};
        \addplot [ name path = C, thick ] {-x + 4};
        \addplot [ name path = D, thick ] {-x + 1};

        \addplot[name path=top,draw=none] {5.3};
        \addplot[name path=bottom,draw=none] {0};

        \addplot[pattern=north west lines,pattern color=blue!30] fill
        between[of=A and top];
        \addplot[pattern=north west lines,pattern color=blue!30] fill
        between[of=C and top];
        \addplot[pattern=north west lines,pattern color=blue!30] fill
        between[of=B and bottom];
        \addplot[pattern=north west lines,pattern color=blue!30] fill
        between[of=D and bottom];
        \addplot[only marks,mark=o] coordinates {
                    (0, 4) 
            (-1, 3) (0, 3) (1, 3)
            (-1, 2) (0, 2) (1, 2)
                    (0, 1) 
        };

        \addplot[fill=red,fill opacity=0.20] fill between [of=B and bottom,soft
        clip={domain=0:1.5}];
        \addplot[fill=red,fill opacity=0.20] fill between [of=D and bottom,soft
        clip={domain=-1.5:0}];
    \end{axis} 
\end{tikzpicture}