How to define and initialize a variable only once in a recursive function?

Question

I am trying to solve the 0/1 Knapsack problem on GeeksforGeeks and it requires me to complete the funtion

int knapSack(int W, int wt[], int val[], int n) 

Now I want to do this with recursion + memoization. But to that I need to define and initialise a DP matrix for every test case. It looks like this.

int dp[1001][1001];
memset(dp,-1,sizeof(dp));

Now What I can think of is define the matrix globally and using memset inside function, but the problem arises is that memset would reset the matrix on every recursive call. Is there a way to get around it? or do I just have to do the tabulation method instead?

Answer 1

Avoid global variable.

Split your method:

int knapSackRec(int (&dp)[1001][1001], int W, int wt[], int val[], int n)
{
    // ...
}

int knapSack(int W, int wt[], int val[], int n)
{
    int dp[1001][1001];
    memset(dp, -1, sizeof (dp));
    return knapSackRec(dp, W, wt, val, n);
}