How to initialize a 2D array with all elements as -1?

Question

I am trying to solve a dynamic programming problem using memoization. I need to declare a 2D array as a global variable and initialise all of its element as -1. Then I am going to use this initialised array in a recursive function.

#include<iostream>
using namespace std;
int dp[1002][1002];
//initialize above array as all of its element = -1

int max_value(int val[], int wt[], int n, int W)
{
    if(n==0 || W==0)
    {
        return 0;
    }
    if(dp[n][W] != -1)
    {
        return dp[n][W];
    }
    if(wt[n-1] <= W)
    {
        return dp[n][W] = max(val[n-1] + max_value(val, wt, n-1, W-wt[n-1]), max_value(val, wt, n-1, W));
    }
    else
    {
        return dp[n][W] = max_value(val, wt, n-1, W);

    }
}

Can you tell me how to initialize all the elements of array dp[][] as -1?

Please do not post the same question, repeatedly. – Sam Varshavchik Jun 10 '20 at 13:59 — Sam Varshavchik, Jun 10 '20 at 13:59

score 1 · Answer 1 · edited Jun 10 '20 at 14:23

1

You can use std::fill

std::fill(&dp[0][0], & dp[1001][1002], -1);

edited Jun 10 '20 at 14:23

JohnFilleau

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answered Jun 10 '20 at 13:58

김선달

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this gives an error `prog.cpp:5:5: error: expected constructor, destructor, or type conversion before ‘(’ token fill(&dp[0][0], & dp[10][10], -1);` – Sachin Kumar Jun 10 '20 at 14:04
I need to initialize array outside of the funcyion – Sachin Kumar Jun 10 '20 at 14:05
@SachinKumar Move it somewhere else. – Thomas Sablik Jun 10 '20 at 14:21
@Sachin you need to initialize the array inside of *a* function. Doesn't need to be this one. Read the linked duplicate question for suggestions. – JohnFilleau Jun 10 '20 at 14:23
@AsteroidsWithWings In it's original form `dp[1002][1002]` was 1003 elemetns past the end. But yes, it's fixed, might as well remove the comment. – Lukas-T Jun 10 '20 at 19:31

How to initialize a 2D array with all elements as -1?

1 Answers1