542 01 Matrix 01 Matrix

Given a matrix of 0s and 1s, find the distance of each element to the nearest 0.
The distance between two adjacent elements is 1.
Example 1:
Input:
0 0 0
0 1 0
0 0 0
Output:
0 0 0
0 1 0
0 0 0

Example 2:
Input:
0 0 0
0 1 0
1 1 1
Output:
0 0 0
0 1 0
1 2 1
Note:
    1. The number of elements of a given matrix should not exceed 10000.
    2. At least one element in the given matrix is ​​0.
    3. Elements in a matrix are adjacent only in four directions: up, down, left, right.
See: https://leetcode.com/problems/01-matrix/description/

C++：

class Solution {
public:
    vector<vector<int>> updateMatrix(vector<vector<int>>& matrix)
    {
        int m = matrix.size(), n = matrix[0].size();
        vector<vector<int>> res(m, vector<int>(n, INT_MAX - 1));
        for (int i = 0; i < m; ++i)
        {
            for (int j = 0; j < n; ++j)
            {
                if (matrix[i][j] == 0)
                {
                    res[i][j] = 0;
                }
                else
                {
                    if (i > 0)
                    {
                        res[i][j] = min(res[i][j], res[i - 1][j] + 1);
                    }
                    if (j > 0)
                    {
                        res[i][j] = min(res[i][j], res[i][j - 1] + 1);
                    }
                }
            }
        }
        for (int i = m - 1; i >= 0; --i)
        {
            for (int j = n - 1; j >= 0; --j)
            {
                if (res[i][j] != 0 && res[i][j] != 1)
                {
                    if (i < m - 1)
                    {
                        res[i][j] = min(res[i][j], res[i + 1][j] + 1);
                    }
                    if (j < n - 1)
                    {
                        res[i][j] = min(res[i][j], res[i][j + 1] + 1);
                    }
                }
            }
        }
        return res;
    }
};

 Reference: https://www.cnblogs.com/grandyang/p/6602288.html