Image Smoother LeetCode solution in Java

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/**
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 * Constant Space Solution. Using input array to store the average This solution can be modified to
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 * work if numbers are upto 2^16 - 1 (65,535).
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 *
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 * <p>Time Complexity: O(8*M*N + M*N) = O(M*N)
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 *
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 * <p>Space Complexity: O(1)
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 *
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 * <p>M = Number of rows. N = Number of columns.
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 *
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 * <p>Note: Similar to "289. Game of Life"
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 */
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class Solution {
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  private static final int[][] DIRS = {
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    {0, 1}, {1, 1}, {1, 0}, {1, -1}, {0, -1}, {-1, -1}, {-1, 0}, {-1, 1}
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  };
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  public int[][] imageSmoother(int[][] img) {
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    if (img == null) {
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      throw new IllegalArgumentException("Input image is null");
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    }
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    if (img.length == 0 || img[0].length == 0) {
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      return img;
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    }
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    int rows = img.length;
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    int cols = img[0].length;
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    if (rows == 1 && cols == 1) {
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      return img;
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    }
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    for (int i = 0; i < rows; i++) {
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      for (int j = 0; j < cols; j++) {
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        int sum = img[i][j];
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        int count = 1;
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        for (int[] d : DIRS) {
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          int x = i + d[0];
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          int y = j + d[1];
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          if (x >= 0 && x < rows && y >= 0 && y < cols) {
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            sum += img[x][y] & 0xFF;
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            count++;
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          }
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        }
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        img[i][j] |= (sum / count) << 8;
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      }
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    }
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    for (int i = 0; i < rows; i++) {
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      for (int j = 0; j < cols; j++) {
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        img[i][j] >>>= 8;
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      }
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    }
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    return img;
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  }
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}