动态规划 dp[i][j]表示A[1...i]和B[1...j]的最小操作 若A[i] == B[j],则dp[i][j] = dp[i-1][j-1]; 若A[i] != B[j],则: 1)A[1...i-1]变为B[1...j],删除A[i],即dp[i][j] = dp[i-1][j] + 1 2)A[1...i]变为B[1...j-1],删除B[j...