leetcode 73:矩阵置0

我的思路是 ，用一个hash set存 每个为0点的坐标，然后取出来后迭代置0； 这样做的话也有毛病：处有重复置0的情况

 

struct VectorHash{
	size_t operator() (const vector<int>& v) const{
		hash<int> hasher;
		size_t seed = 0;
		for(int i: v){
			seed ^= hasher(i) + 0x9e3779b9 + (seed << 6) + (seed >>2);
		}
		return seed;
	}
};
struct Equal_Vector{
	bool operator()(const vector<int>& v1, const vector<int>& v2 ) const{
		return v1[0] == v2[0] && v1[1] == v2[1];
	}
};
class Solution {
public:
    void setZeroes(vector<vector<int> >& matrix) {
    	int rows = matrix.size();
    	if(rows == 0){
    		return ;
    	}
    	int cols = matrix[0].size();
    	if(cols == 0){
    		return ;
    	}
    	// cout << " * "<< endl;
    	unordered_set<vector<int>, VectorHash, Equal_Vector> zero_pos;
    	for(int i=0; i<rows; ++i){
    		for(int j=0; j<cols; ++j){
    			if(matrix[i][j] == 0){
    				vector<int> temp;
    				temp.push_back(i);
    				temp.push_back(j);
    				zero_pos.insert(temp);
    				
    			}
    		}
    	}
    	for(unordered_set<vector<int>,VectorHash, Equal_Vector >::iterator ite = zero_pos.begin(); ite != zero_pos.end(); ++ite){
    		int r = (*ite)[0];
    		int l = (*ite)[1];
    		// r -> 0
    		for(int i=0; i<cols ;++i){
    			matrix[r][i] = 0;
    		}
    		// l -> 0
    		for(int i=0; i<rows; ++i){
    			matrix[i][l] = 0;
    		}
    	}
    }
};

 

其他解法：

先找行首列首是否有0，   用两个变量记录一下：是否要把行首、列首置零；

然后利用行首和列首 存当前矩阵  （该列。改行）是否置零的信息；

class Solution {
    public void setZeroes(int[][] matrix) {
        boolean rowFlag = false;
        //判断首行
        for (int i = 0; i < matrix[0].length; i++) {
            if (matrix[0][i] == 0) {
                rowFlag = true;
                break;
            }
        }

        boolean colFlag = false;
        for (int i = 0; i < matrix.length; i++) {
            if (matrix[i][0] == 0) {
                colFlag = true;
                break;
            }
        }

        for (int i = 1; i < matrix.length; i++) {
            for (int j = 1; j < matrix[0].length; j++) {
                if (matrix[i][j] == 0){
                    matrix[i][0] = 0;
                    matrix[0][j] = 0;
                }
            }
        }

        for (int i = 1; i < matrix[0].length; i++) {
            if (matrix[0][i] == 0) {
                for (int j = 0; j < matrix.length; j++) {
                    matrix[j][i] = 0;
                }
            }
        }

        for (int i = 1; i < matrix.length; i++) {
            if (matrix[i][0] == 0) {
                for (int j = 0; j < matrix[0].length; j++) {
                    matrix[i][j] = 0;
                }
            }
        }
        if (rowFlag){
            for (int i = 0; i < matrix[0].length; i++) {
                matrix[0][i] = 0;
            }
        }
        if (colFlag){
            for (int i = 0; i < matrix.length; i++) {
                matrix[i][0] = 0;
            }
        }
    }
}