2938_separate_black_and_white_balls.java

class Solution {
    public long minimumSteps(String s) {
        long swap = 0;
        int b = 0; 
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '0') 
                swap += (long) b; 
            else
                b++; 
        }
        return swap;
    }
}