[LeetCode] 73. Set Matrix Zeroes

[LeetCode] 73. Set Matrix Zeroes

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Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

Follow up:
Did you use extra space?
A straight forward solution using O(mn) space is probably a bad idea.
A simple improvement uses O(m + n) space, but still not the best solution.
Could you devise a constant space solution?

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題意是把數組中爲0的位置對應的行和列都設爲0。

思路： 想了很久都沒想到O(1)空間複雜度，太蠢了，就先用O(m+n)的空間複雜度硬爆先吧。
用兩個數組分別記錄爲0的行和列的下標，然後最後遍歷的時候設0。

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class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        int leni = matrix.size();
        if (leni == 0) {
            return;
        }

        vector<int> is0i;
        vector<int> is0j;


        int lenj = matrix[0].size();

        for (int i=0; i<leni; ++i) {
            for (int j=0; j<lenj; ++j) {
                if (matrix[i][j] == 0) {
                    is0i.push_back(i);
                    is0j.push_back(j);
                }
            }
        }

        for (int i=0; i<is0i.size(); ++i) {
            for (int j=0; j<lenj; ++j) {
                matrix[is0i[i]][j] = 0;
            }
        }

        for (int j=0; j<is0j.size(); ++j) {
            for (int i=0; i<leni; ++i) {
                matrix[i][is0j[j]] = 0;
            }
        }
    }
};

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然後去Discuss學習了一波，人家把記錄這些信息的都放在matrix的第一行和第一列，然後用兩個boolean值來特別處理第一行和第一列即可。