1475.Final prices with a special discount in a shop

class Solution {
    static class pair{
        int a;
        int b;
        pair(int a,int b){
            this.a=a;
            this.b=b;
        }
    }
    public int[] finalPrices(int[] prices) {
        Stack<pair> stack=new Stack<>();
        stack.push(new pair(prices[0],0));
        for(int i=1;i<prices.length;i++){
            while(!stack.isEmpty() && stack.peek().a>=prices[i]){
                prices[stack.peek().b]=stack.peek().a-prices[i];
                stack.pop();
            }
            stack.add(new pair(prices[i],i));
        }
        return prices;   
    }
}