LeetCode63. 不同路径 II

//63. 不同路径 II
//算是dp吧，最简单的dp实现
class Solution {
public:
  int uniquePathsWithObstacles(vector<vector<int>>& grid) {
    int n = grid.size();
    if (n == 0) return 0;
    int m = grid[0].size();
    if (m == 0) return 0;
    vector<vector<int>>f(n + 1, vector<int>(m + 1, 0));
    f[1][1] = 1;
    for (int i = 1; i <= n; i++)
      for (int j = 1; j <= m; j++)
        if (grid[i - 1][j - 1]) f[i][j] = 0;
        else f[i][j] += f[i - 1][j] + f[i][j - 1];
    return f[n][m];
  }
};
//按照背包的方法，把空间优化一下
class Solution {
public:
  int uniquePathsWithObstacles(vector<vector<int>>& grid) {
    int n = grid.size();
    if (n == 0) return 0;
    int m = grid[0].size();
    if (m == 0) return 0;
    vector<int>f(m + 1, 0);
    f[1] = 1;
    for (int i = 1; i <= n; i++)
      for (int j = 1; j <= m; j++)
        if (grid[i - 1][j - 1]) f[j] = 0;
        else f[j] += f[j - 1];
    return f[m];
  }
};