弗洛伊德（Floyd）算法

for k = 1 to n do
  for i = 1 to n do
    for j = 1 to n do
      if (Di,j>Di,k + Dk,j) then
        Di,j = Di,k + Dk,j;

参考：http://zh.wikipedia.org/zh-cn/Floyd-Warshall%E7%AE%97%E6%B3%95