问题描述
Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.)
You have the following 3 operations permitted on a word:
a) Insert a character
b) Delete a character
c) Replace a character
经典DP问题。
dp[i][j]：表示从s1[0…i-1] 变到 s2[0…j-1]所需要的最少操作次数，其中可以看出i,j≥1。
