c++之vector

二维vector初始化

• 方法一

   int nums = 5;
   int a[5][5] = {{0, 10, -1, 4, 12},
                  {10, 0, 15, 8, 5},
                  {-1, 15, 0, 7, 30},
                  {4, 8, 7, 0, 6},
                  {12, 5, 30, 6, 0}};
   vector<vector<int> > graph(nums); //创建一个vector元素个数为nums
   for(int i = 0; i < nums; ++i){
      graph[i].resize(nums); //分配内存 值全为0
   }
   for(int i = 0; i < nums; ++i){
      for(int j = 0; j < nums; ++j){
         graph[i][j] = a[i][j];
      }
   }

• 方法二

   int nums = 5;
   int a[5][5] = {{0, 10, -1, 4, 12},
                  {10, 0, 15, 8, 5},
                  {-1, 15, 0, 7, 30},
                  {4, 8, 7, 0, 6},
                  {12, 5, 30, 6, 0}};
   vector<vector<int> > obj(nums, vector<int>(nums));
   for(int i = 0; i < nums; ++i){
      for(int j = 0; j < nums; ++j){
         graph[i][j] = a[i][j];
      }
   }

vector.resize()的应用

例如生成杨辉三角：

vector<vector<int>> generate(int numRows) {
        vector<vector<int>> result(numRows);
        for(int i = 0; i < numRows; ++i){
            result[i].resize(i+1); //resize()操作：创建指定数量的的元素并指定vector的存储空间
            result[i][0] = result[i][i] = 1;
            for(int j = 1; j < i; ++j){
                result[i][j] = result[i-1][j-1] + result[i-1][j];
            }
        }
        return result;
    }