<Solution video>


<YOUKU>

Performanc  https://v.youku.com/v_show/id_XNDE0MzkyNjQxMg==.html?spm=a2h3j.8428770.3416059.1
Explanation  https://v.youku.com/v_show/id_XNDE0Mzk0MDQ0MA==.html?spm=a2h3j.8428770.3416059.1