63. Unique Paths II

LeetCode

Dynamic Programming

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class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;
        int[][] dp = new int[m][n];

        // update first row and column
        for (int i = 0; i < m; i++) {
            if (obstacleGrid[i][0] == 1) {
                dp[i][0] = 0;
                break;
            }
            dp[i][0] = 1;
        }
        for (int j = 0; j < n; j++) {
            if (obstacleGrid[0][j] == 1) {
                dp[0][j] = 0;
                break;
            }
            dp[0][j] = 1;
        }

        // calculate from (1,1)
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (obstacleGrid[i][j] == 1) {
                    dp[i][j] = 0;
                } else {
                    dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
                }
                
            }
        }

        return dp[m - 1][n - 1];

    }
}

Remarks:

  1. Adapted from No. 62.
  2. TC: $O(m\times n)$, SC: $O(m\times n)$.