深度/广度优先搜索LeetCode 542 01 Matrix

LeetCode 542

01 Matrix

• Reference: http://www.cnblogs.com/grandyang/p/6602288.html
• Problem Description：
  给出一个0和1组成的矩阵，计算矩阵中每一元素到0的最短路径。
  具体的题目信息：
  https://leetcode.com/problems/01-matrix/description/
• Solution: 采用队列辅助实现深度/广度优先搜索

class Solution {
public:
    vector<vector<int>> updateMatrix(vector<vector<int>>& matrix) {
    //res记录四个方向
        vector<pair<int, int>> res = {{0, -1}, {0, 1}, {1, 0}, {-1, 0}}; 
        queue<pair<int, int>> q;
        for (int i = 0; i < matrix.size(); i++) {
            for (int j = 0; j < matrix[0].size(); j++) {
                if (matrix[i][j] == 0) q.push({i, j});
                else matrix[i][j] = INT_MAX;
            }
        }
        while(!q.empty()) {
            pair<int, int> t = q.front();
            q.pop();
            for (int i = 0; i < res.size(); i++) {
                int x = t.first+res[i].first;
                int y = t.second+res[i].second;
                if (x < 0 || x >= matrix.size() || y < 0 || y >= matrix[0].size() ||matrix[x][y]<=matrix[t.first][t.second]) continue;
                matrix[x][y] = matrix[t.first][t.second]+1;
                q.push({x, y});
            }
        }
        return matrix;
    }
};