解析

class Solution {
public:
  void setZeroes(vector<vector<int>> &matrix) {
    if (matrix.empty()) {
      return;
    }
    int m = matrix.size();
    int n = matrix[0].size();
    bool firstRowZeroFlag = false;
    bool firstColumnZeroFlag = false;
    for (int i = 0; i < m; ++i) {
      if (matrix[i][0] == 0) {
        firstColumnZeroFlag = true;
      }
    }
    for (int j = 0; j < n; ++j) {
      if (matrix[0][j] == 0) {
        firstRowZeroFlag = true;
      }
    }

    for (int i = 1; i < m; ++i) {
      for (int j = 1; j < n; ++j) { // i,j从1开始，标签行和标签列先不动
        if (matrix[i][j] == 0) {
          matrix[i][0] = matrix[0][j] = 0;
        }
      }
    }
    for (int i = 1; i < m; ++i) {
      for (int j = 1; j < n; ++j) {
        if (matrix[i][0] == 0 || matrix[0][j] == 0) {
          matrix[i][j] = 0;
        }
      }
    }

    if (firstColumnZeroFlag) {
      for (int i = 0; i < m; ++i) {
        matrix[i][0]=0;
      }
    }
    if (firstRowZeroFlag) {
      for (int j = 0; j < n; ++j) {
        matrix[0][j]=0;
      }
    }
  }
};