class Solution {
    public int minimumTotal(List<List<Integer>> grid) {

        int numRows = grid.size();
        for(int row = 1; row < numRows; row++) {
            int leftWall = grid.get(row-1).get(0) + grid.get(row).get(0);
            grid.get(row).set(0, leftWall);

            int rightWall = grid.get(row-1).get(row-1) + grid.get(row).get(row);
            grid.get(row).set(row, rightWall);
        }

        for(int row = 2; row < numRows; row++) {
            for(int col = 1; col < row; col++) {
                int min = Math.min(grid.get(row-1).get(col), grid.get(row-1).get(col-1));
                int curr = min + grid.get(row).get(col);
                grid.get(row).set(col, curr);
            }
        }

        List<Integer> lastRow = grid.get(grid.size()-1);
        return Collections.min(lastRow);

    }
}