題目：62. Unique Paths

連結：https://leetcode.com/problems/unique-paths/description/

• 等級：Medium

class Solution {
    public int uniquePaths(int m, int n) {
        int[][] dp = new int[m][n];
        
        for (int i = 0; i < m; i++) {
            dp[i][0] = 1;
        }
        for (int j = 0; j < n; j++) {
            dp[0][j] = 1;
        }
        
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                dp[i][j] = dp[i-1][j] + dp[i][j-1];
            }
        }
        
        return dp[m-1][n-1];
    }
}

• Time complexity: O(m*n)
• Space complexity: O(m*n)

題目：63. Unique Paths II

連結：https://leetcode.com/problems/unique-paths-ii/description/

• 等級：Medium

class Solution {
    public int uniquePathsWithObstacles(int[][] A) {
        int n = A.length;
        int m = A[0].length;
        int [][] ans = new int[n][m];
        for(int i = 0;i<n;i++){
            if(A[i][0] == 0) ans[i][0] = 1;
            else break;
        }
        for(int j = 0;j<m;j++){
            if(A[0][j] == 0) ans[0][j] = 1;
            else break;
        }

        for(int i = 1;i<n;i++){
            for(int j = 1;j<m;j++){
                if(A[i][j]==0) ans[i][j] = ans[i-1][j]+ans[i][j-1];
            }
        }
        return ans[n-1][m-1];
    }
}

• Time complexity: O(m*n)
• Space complexity: O(m*n)