Dungeon Game LeetCode solution in Java

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class Solution {
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  Integer[][] min;
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  public int calculateMinimumHP(int[][] dungeon) {
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    min = new Integer[dungeon.length][dungeon[0].length];
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    int answer = min(0, 0, dungeon);
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    return Math.max(answer, 1);
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  }
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  public int min(int i, int j, int[][] dungeon) {
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    if (i > dungeon.length - 1 || j > dungeon[0].length - 1) return 400000;
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    if (i == dungeon.length - 1 && j == dungeon[0].length - 1) return -dungeon[i][j] + 1;
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    if (min[i][j] == null) {
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      int down = min(i + 1, j, dungeon);
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      int right = min(i, j + 1, dungeon);
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      min[i][j] = Math.min(Math.max(right, 1), Math.max(down, 1)) - dungeon[i][j];
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    }
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    return min[i][j];
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  }
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}