LeetCode 0661. Image Smoother Solution in Java, Python, C++, JavaScript, Go & Rust | Explanation + Code

Description

An image smoother is a filter of the size 3 x 3 that can be applied to each cell of an image by rounding down the average of the cell and the eight surrounding cells (i.e., the average of the nine cells in the blue smoother). If one or more of the surrounding cells of a cell is not present, we do not consider it in the average (i.e., the average of the four cells in the red smoother).

Given an m x n integer matrix img representing the grayscale of an image, return the image after applying the smoother on each cell of it.

 

Example 1:

Input: img = [[1,1,1],[1,0,1],[1,1,1]]
Output: [[0,0,0],[0,0,0],[0,0,0]]
Explanation:
For the points (0,0), (0,2), (2,0), (2,2): floor(3/4) = floor(0.75) = 0
For the points (0,1), (1,0), (1,2), (2,1): floor(5/6) = floor(0.83333333) = 0
For the point (1,1): floor(8/9) = floor(0.88888889) = 0

Example 2:

Input: img = [[100,200,100],[200,50,200],[100,200,100]]
Output: [[137,141,137],[141,138,141],[137,141,137]]
Explanation:
For the points (0,0), (0,2), (2,0), (2,2): floor((100+200+200+50)/4) = floor(137.5) = 137
For the points (0,1), (1,0), (1,2), (2,1): floor((200+200+50+200+100+100)/6) = floor(141.666667) = 141
For the point (1,1): floor((50+200+200+200+200+100+100+100+100)/9) = floor(138.888889) = 138

 

Constraints:

• m == img.length
• n == img[i].length
• 1 <= m, n <= 200
• 0 <= img[i][j] <= 255

Solutions

Solution 1: Direct Traversal

We create a 2D array ans of size m × n, where ans[i][j] represents the smoothed value of the cell in the i-th row and j-th column of the image.

For ans[i][j], we traverse the cell in the i-th row and j-th column of img and its surrounding 8 cells, calculate their sum s and count cnt, then compute the average value s / cnt and store it in ans[i][j].

After the traversal, we return ans.

The time complexity is O(m × n), where m and n are the number of rows and columns of img, respectively. Ignoring the space consumption of the answer array, the space complexity is O(1).

PythonJavaC++GoTypeScriptRust

class Solution: def imageSmoother(self, img: List[List[int]]) -> List[List[int]]: m, n = len(img), len(img[0]) ans = [[0] * n for _ in range(m)] for i in range(m): for j in range(n): s = cnt = 0 for x in range(i - 1, i + 2): for y in range(j - 1, j + 2): if 0 <= x < m and 0 <= y < n: cnt += 1 s += img[x][y] ans[i][j] = s // cnt return ans(code-box)

class Solution { public int[][] imageSmoother(int[][] img) { int m = img.length; int n = img[0].length; int[][] ans = new int[m][n]; for (int i = 0; i < m; ++i) { for (int j = 0; j < n; ++j) { int s = 0; int cnt = 0; for (int x = i - 1; x <= i + 1; ++x) { for (int y = j - 1; y <= j + 1; ++y) { if (x >= 0 && x < m && y >= 0 && y < n) { ++cnt; s += img[x][y]; } } } ans[i][j] = s / cnt; } } return ans; } }(code-box)

class Solution { public: vector<vector<int>> imageSmoother(vector<vector<int>>& img) { int m = img.size(), n = img[0].size(); vector<vector<int>> ans(m, vector<int>(n)); for (int i = 0; i < m; ++i) { for (int j = 0; j < n; ++j) { int s = 0, cnt = 0; for (int x = i - 1; x <= i + 1; ++x) { for (int y = j - 1; y <= j + 1; ++y) { if (x < 0 || x >= m || y < 0 || y >= n) { continue; } ++cnt; s += img[x][y]; } } ans[i][j] = s / cnt; } } return ans; } };(code-box)

func imageSmoother(img [][]int) [][]int { m, n := len(img), len(img[0]) ans := make([][]int, m) for i, row := range img { ans[i] = make([]int, n) for j := range row { s, cnt := 0, 0 for x := i - 1; x <= i+1; x++ { for y := j - 1; y <= j+1; y++ { if x >= 0 && x < m && y >= 0 && y < n { cnt++ s += img[x][y] } } } ans[i][j] = s / cnt } } return ans }(code-box)

function imageSmoother(img: number[][]): number[][] { const m = img.length; const n = img[0].length; const ans: number[][] = Array.from({ length: m }, () => Array(n).fill(0)); for (let i = 0; i < m; ++i) { for (let j = 0; j < n; ++j) { let s = 0; let cnt = 0; for (let x = i - 1; x <= i + 1; ++x) { for (let y = j - 1; y <= j + 1; ++y) { if (x >= 0 && x < m && y >= 0 && y < n) { ++cnt; s += img[x][y]; } } } ans[i][j] = Math.floor(s / cnt); } } return ans; }(code-box)

impl Solution { pub fn image_smoother(img: Vec<Vec<i32>>) -> Vec<Vec<i32>> { let m = img.len(); let n = img[0].len(); let mut ans = vec![vec![0; n]; m]; for i in 0..m { for j in 0..n { let mut s = 0; let mut cnt = 0; for x in i.saturating_sub(1)..=(i + 1).min(m - 1) { for y in j.saturating_sub(1)..=(j + 1).min(n - 1) { s += img[x][y]; cnt += 1; } } ans[i][j] = s / cnt; } } ans } }(code-box)