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  • [LeetCode] Set Matrix Zeroes 解题报告


    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?
    » Solve this problem

    [解题思路]
    非常无聊的一道题。解题点就在于清空标志位存在哪里的问题。可以创建O(m+n)的数组来存储,但此题是希望复用已有资源。这里可以选择第一行和第一列来存储标志位。

    1.先确定第一行和第一列是否需要清零
    2.扫描剩下的矩阵元素,如果遇到了0,就将对应的第一行和第一列上的元素赋值为0
    3.根据第一行和第一列的信息,已经可以讲剩下的矩阵元素赋值为结果所需的值了
    4.根据1中确定的状态,处理第一行和第一列。


    [Code]
    1:    void setZeroes(vector<vector<int> > &matrix) {  
    2: // Start typing your C/C++ solution below
    3: // DO NOT write int main() function
    4: assert(matrix.size()>0);
    5: int row = matrix.size(), col = matrix[0].size();
    6: bool zerorow=false, zerocol=false;
    7: for(int i = 0; i< col; i++)
    8: if(matrix[0][i] ==0)
    9: zerorow = 1;
    10: for(int i = 0; i< row; i++)
    11: if(matrix[i][0] ==0)
    12: zerocol=1;
    13: for(int i =1; i < row; i++)
    14: for(int j = 1; j<col; j++)
    15: if(matrix[i][j] ==0)
    16: {
    17: matrix[0][j] =0;
    18: matrix[i][0] =0;
    19: }
    20: for(int i =1; i < row; i++)
    21: for(int j = 1; j<col; j++)
    22: if(matrix[i][0] ==0 || matrix[0][j] ==0)
    23: matrix[i][j] =0;
    24: if(zerorow ==1)
    25: for(int i =0; i< col; i++)
    26: matrix[0][i] =0;
    27: if(zerocol==1)
    28: for(int i =0; i< row; i++)
    29: matrix[i][0] =0;
    30: }




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  • 原文地址:https://www.cnblogs.com/codingtmd/p/5078954.html
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