2026/04/24

[LeetCode] 73 Set Matrix Zeroes

 要求額外空間要是常數

用row0/col0 來存對應的row/col要不要清零

再用兩個變數來存row0/col0要不要清零

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class Solution {
public:
  void setZeroes(vector<vector<int>>& matrix) {
    int N = matrix.size();
    int M = matrix[0].size();
    bool isFirstColZero = false;
    bool isFirstRowZero = false;

    for (int i = 0; i < N; i++)
      if (matrix[i][0] == 0)
        isFirstColZero = true;

    for (int i = 0; i < M; i++)
      if (matrix[0][i] == 0)
        isFirstRowZero = true;
    
    for (int i = 1; i < N; i++) 
      for (int j = 1; j < M; j++)
        if (matrix[i][j] == 0) {
          matrix[i][0] = 0;
          matrix[0][j] = 0;
        }

    for (int i = 1; i < N; i++) 
      for (int j = 1; j < M; j++)
        if (matrix[i][0] == 0 || matrix[0][j] == 0)
          matrix[i][j] = 0;
    
    if (isFirstColZero)
      for (int i = 0; i < N; i++)
        matrix[i][0] = 0;
    
    if (isFirstRowZero)
      for (int i = 0; i < M; i++)
        matrix[0][i] = 0;
  }
};
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