LeetCode之Unique Paths

/*备忘录法。*/
class Solution {
public:
	int uniquePaths(int m, int n) {
		if(m < 1 || n < 1) return 0;
		vector<vector<int> > path(m+1, vector<int>(n+1, 0));
		for(int i = 1; i <= m; ++i){
			for(int j = 1; j <= n; ++j){
				path[i][j] = dfs(i, j, path);
			}
		}
		return path[m][n];
	}

	int dfs(int row, int col, vector<vector<int> > &path){
		if(row == 1 || col == 1) return 1;
		else return get(row-1, col, path) + get(row, col-1, path);
	}

	int get(int row, int col, vector<vector<int> > &path){
		if(row == 1 || col == 1) return 1;
		if(path[row][col] > 0) return path[row][col];
		else return dfs(row, col, path);
	}
};

/*动态规划法。*/
class Solution {
public:
	int uniquePaths(int m, int n) {
		if(m < 1 || n < 1) return 0;
		vector<int> path(n+1, 0);
		path[1] = 1;
		for(int i = 1; i <= m; ++i){
			for(int j = 2; j <= n; ++j){
				path[j] = path[j] + path[j-1];
			}
		}
		return path[n];
	}
};