刷题编程基础

建立二维数组：
C++ int dp[101][101];
JAVA int[][] dp = new int[m][n];
dp=[[0 for k1 in rang n] for k2 in range(m)]

s[::-1] python切片的格式[start🔚step]

```python
a = [1,2,3,4,5]
b = a[:]
b[0] = 100
print(a) # [1,2,3,4,5]
print(b) # [100,2,3,4,5]