631. Design Excel Sum Formula

Explanation:

To design Excel sum formula, we can use a two-dimensional array to store the values of cells in the Excel grid. We can also maintain a mapping from cell names to their corresponding row and column indices for easy access. When a cell's value is updated, we need to recursively update all the dependent cells that reference the updated cell in their formulas.

Algorithm:

Create a two-dimensional array to store cell values.
Create a mapping from cell names to their corresponding row and column indices.
Implement a function to update cell value:
- If the cell contains a number, update its value.
- If the cell contains a formula, evaluate the formula by recursively calculating the values of referenced cells.
Implement a function to get the value of a cell:
- If the cell contains a number, return the number.
- If the cell contains a formula, evaluate the formula by recursively calculating the values of referenced cells.

Time Complexity:

Updating a cell: O(N), where N is the number of cells dependent on the updated cell.
Getting the value of a cell: O(1).

Space Complexity:

O(R * C) for storing cell values, where R is the number of rows and C is the number of columns.
O(N) for maintaining the mapping of cell names to indices.

: :

View Leetcode Problem

class Excel {
    private int[][] grid;
    private Map<String, List<String>> formulaMap;

    public Excel(int H, char W) {
        grid = new int[H][W - 'A' + 1];
        formulaMap = new HashMap<>();
    }

    public void set(int r, char c, int v) {
        grid[r - 1][c - 'A'] = v;
        updateDependents(r, c);
    }

    private void updateDependents(int r, char c) {
        String cellName = "" + c + r;
        if (formulaMap.containsKey(cellName)) {
            for (String dependent : formulaMap.get(cellName)) {
                int dependentR = dependent.charAt(1) - '0';
                char dependentC = dependent.charAt(0);
                grid[dependentR - 1][dependentC - 'A'] = evaluateFormula(dependentR, dependentC);
                updateDependents(dependentR, dependentC);
            }
        }
    }

    private int evaluateFormula(int r, char c) {
        int sum = 0;
        String cellName = "" + c + r;
        for (String reference : formulaMap.get(cellName)) {
            int refR = reference.charAt(1) - '0';
            char refC = reference.charAt(0);
            if (Character.isDigit(refC))
                sum += Integer.parseInt(reference);
            else
                sum += grid[refR - 1][refC - 'A'];
        }
        return sum;
    }

    public int get(int r, char c) {
        return grid[r - 1][c - 'A'];
    }

    public void set(String r, char c, String[] strs) {
        String cellName = "" + c + r;
        formulaMap.put(cellName, new ArrayList<>(Arrays.asList(strs)));
        grid[r - 1][c - 'A'] = evaluateFormula(r, c);
        updateDependents(r, c);
    }
}

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