创建：
int **dp = new int *[x+1]; for(i=0;i<=x;i++) dp[i] = new int[y+1];
销毁：
for(i=0;i<=x;i++) delete []dp[i]; delete []dp;
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创建二维动态数组
Keep it simple!
创建：
int **dp = new int *[x+1]; for(i=0;i<=x;i++) dp[i] = new int[y+1];
销毁：
for(i=0;i<=x;i++) delete []dp[i]; delete []dp;
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