编辑距离
INPUT:two words are represented by two char array a,b
OUTPUT:edit distance between a and b
create an empty 2-dim E[1...m][1...n]
for i=1...m do
E[i][0] 对应 i
for j=1...n do
E[0][j] 对应 j
设立一个k对应a[i]!=a[j]
E[i][j] 的最小情况就是 E[i-1][j]+1, E[i][j-1]+1, E[i-1][j-1]+k
return E[m][n]