542. 01 Matrix

/*Given a matrix consists of 0 and 1, find the distance of the nearest 0 for each cell.The distance between two adjacent cells is 1.Example 1: Input:0 0 00 1 00 0 0Output:0 0 00 1 00 0 0Example 2: Input:0 0 00 1 01 1 1Output:0 0 00 1 01 2 1Note:The number of elements of the given matrix will not exceed 10,000.There are at least one 0 in the given matrix.The cells are adjacent in only four directions: up, down, left and right.*/class Solution {public:    vector<vector<int>> updateMatrix(vector<vector<int>>& matrix) {        if(matrix.empty()) return matrix;        int m=matrix.size(),n=matrix[0].size();        queue<pair<int,int>> q;        for(int i=0;i<m;i++)            for(int j=0;j<n;j++)                if(matrix[i][j]==0)                    q.push(make_pair(i,j));                else                    matrix[i][j]=m+n;        vector<pair<int,int>> dir={{1,0},{-1,0},{0,1},{0,-1}};        while(!q.empty()){            pair<int,int> tmp=q.front();            q.pop();            for(int k=0;k<dir.size();k++){                int r=dir[k].first + tmp.first;                int c=dir[k].second + tmp.second;                if(r>=0 && r<m && c>=0 && c<n && (matrix[r][c]>=matrix[tmp.first][tmp.second]+1)){                    matrix[r][c]=matrix[tmp.first][tmp.second]+1;                    q.push(make_pair(r,c));                }            }        }        return matrix;    }};