MatrixCellsInDistanceOrder.cpp

// Source : https://leetcode.com/problems/matrix-cells-in-distance-order/
// Author : Hao Chen
// Date   : 2019-04-21

/***************************************************************************************************** 
 *
 * We are given a matrix with R rows and C columns has cells with integer coordinates (r, c), where 0 
 * <= r < R and 0 <= c < C.
 * 
 * Additionally, we are given a cell in that matrix with coordinates (r0, c0).
 * 
 * Return the coordinates of all cells in the matrix, sorted by their distance from (r0, c0) from 
 * smallest distance to largest distance.  Here, the distance between two cells (r1, c1) and (r2, c2) 
 * is the Manhattan distance, |r1 - r2| + |c1 - c2|.  (You may return the answer in any order that 
 * satisfies this condition.)
 * 
 * Example 1:
 * 
 * Input: R = 1, C = 2, r0 = 0, c0 = 0
 * Output: [[0,0],[0,1]]
 * Explanation: The distances from (r0, c0) to other cells are: [0,1]
 * 
 * Example 2:
 * 
 * Input: R = 2, C = 2, r0 = 0, c0 = 1
 * Output: [[0,1],[0,0],[1,1],[1,0]]
 * Explanation: The distances from (r0, c0) to other cells are: [0,1,1,2]
 * The answer [[0,1],[1,1],[0,0],[1,0]] would also be accepted as correct.
 * 
 * Example 3:
 * 
 * Input: R = 2, C = 3, r0 = 1, c0 = 2
 * Output: [[1,2],[0,2],[1,1],[0,1],[1,0],[0,0]]
 * Explanation: The distances from (r0, c0) to other cells are: [0,1,1,2,2,3]
 * There are other answers that would also be accepted as correct, such as 
 * [[1,2],[1,1],[0,2],[1,0],[0,1],[0,0]].
 * 
 * Note:
 * 
 * 	1 <= R <= 100
 * 	1 <= C <= 100
 * 	0 <= r0 < R
 * 	0 <= c0 < C
 * 
 ******************************************************************************************************/

class Solution {
public:
    void put(int R, int C, int r, int c, vector<vector<int>>& res) {
        if (r>=0 && r < R && c>=0 && c<C ) {
            res.push_back({r,c});
        }
    }
    vector<vector<int>> allCellsDistOrder(int R, int C, int r0, int c0) {
        int n =  R+C-2;
        vector<vector<int>> result;
        result.push_back({r0,c0});
        for(int i=1; i<= n; i++) {
            // from (r0-i, c0) to (r0, c0+i)
            for(int r=r0-i,c=c0;r!=r0; r++, c++)  put (R, C, r ,c, result);

            // from  (r0, c0+i) to (r0+i, c0)
            for(int r=r0, c=c0+i; c!=c0; r++, c-- ) put (R, C, r, c, result);

            // from (r0+i, c0) to (r0, c0-i)
            for (int r=r0+i, c=c0; r!=r0; r--, c--) put (R, C, r, c, result);

            // from (r0, c0-i) to (r0-i, c0)
            for (int r=r0, c=c0-i; c!=c0; r--, c++) put (R, C, r, c, result);
        }

        return result;
    }
};