CODEWITHSUNDEEP
javaalgorithmdynamic-programmingindexoutofboundsexception
monch
monch

Reputation: 1

How can I solve java.lang.ArrayIndexOutOfBoundsException error in Java

I'm solving a challenge about making an algorithm.

There is a game of land. The Land of Landing game consists of 4 rows in total N rows, with scores in all the columns. When stepping down from the first row, down one row, you must step down on one of the four squares of each row.
However, there is a special rule that can not be repeated in the same row when landing one row at a time.

For example,

| 1 | 2 | 3 | 5 |

| 5 | 6 | 7 | 8 |

| 4 | 3 | 2 | 1 |

If you have stepped on line 1 through line 4 (5), you can not step on line 4 (8) on line 2.

I was trying to use Dynamic Programming in Java.

import java.lang.Math;
import java.util.*;
class Solution {
   int [][] dp = new int[100001][4];

   int solution(int[][] land) {
    int r = land.length;
    for (int i = 0; i < 4; i++)
    {
        dp[0][i] = land[0][i];
    }

    for (int i = 0; i <r; i++)
    {
        for (int j = 0; j < 4; ++j)
        {
            for(int k = 0; k < 4; ++k)
            {
                if (j != k)
                {
                    dp[i][j] = Math.max(dp[i][j], land[i][j] + dp[i-1][k]);
                }
            }
        }
    }
    int ans = 0;
    for (int i = 0; i < 4; ++i)
    {
        ans = Math.max(ans, dp[r-1][i]);
    }
    return ans;
   }
}

it shows error

java.lang.ArrayIndexOutOfBoundsException: -1

I was thinking that it was probably something wrong with the Conditional statement.

In C++, these conditional statements are right. It's running perfect. Why am I getting an error in Java? Is there any difference using array between Java and C++?

Can you please tell me how can I solve this error?

Upvotes: 0

Views: 219

Answers (1)

kosa
kosa

Reputation: 66637

dp[i-1][k] - i starts from ZERO in upper loop, so results of this expression becomes -1 as index.

Java array index starts from ZERO, not -1, which is why ArrayIndexOutOfBoundsException.

I don't know the business case, but one way to solve this is, start first for loop from 1 instead 0.

Upvotes: 1

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