554. Brick Wall

class Solution {
    public int leastBricks(List<List<Integer>> wall) {
        int untouched =0;
        Map<Integer,Integer> map =new HashMap<>();
        
        for(List<Integer> row : wall){
            
            int end=0;
            for(int brick=0 ; brick < row.size() - 1 ; brick++){
                end += row.get(brick);
                map.put(end, map.getOrDefault(end,0) + 1);
                untouched = Math.max(untouched,map.get(end));
            }
        }
        
        return wall.size() - untouched;
    }
}