leetcode刷题记录 5

public class  {
    public int minimumTotal(List<List<Integer>> triangle) {
        int n = triangle.size();
        int[] sum = new int[n];

        
        for (int i = 0; i < n; i++) {
            sum[i] = triangle.get(n - 1).get(i);
        }

        // 自底向上递推，更新sum[]
        for (int i = n - 2; i >= 0; i--) {
            for (int j = 0; j <= i; j++) {
                sum[j] = triangle.get(i).get(j) + Math.min(sum[j], sum[j + 1]);
            }
        }

        return sum[0];
    }
}

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

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

        for (int i = 0; i < m; i++) {
            if (obstacleGrid[i][0] == 1) {
                break;
            }
            grid[i][0] = 1;
        }
        for (int j = 0; j < n; j++) {
            if (obstacleGrid[0][j] == 1) {
                break;
            }
            grid[0][j] = 1;
        }

        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (obstacleGrid[i][j] == 1) {
                    grid[i][j] = 0;
                } else {
                    grid[i][j] = grid[i - 1][j] + grid[i][j - 1];
                }
            }
        }

        return grid[m - 1][n - 1];
    }
}