BuyTwoItems

import java.util.*;

class Solution {
    public int solve(List<Integer> price, int a, int b) {
        Collections.sort(price);
        int count = 0;
        int n = price.size();

        for (int i = 0; i < n; i++) {
            int target1 = a - price.get(i);
            int target2 = b - price.get(i);

            int left = i + 1;
            int right = n - 1;

            int lowerBound = lowerBound(price, left, right, target1);
            int upperBound = upperBound(price, left, right, target2);

            count += upperBound - lowerBound + 1;
        }

        return count;
    }

    private int lowerBound(List<Integer> price, int left, int right, int target) {
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (price.get(mid) >= target) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }

    private int upperBound(List<Integer> price, int left, int right, int target) {
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (price.get(mid) > target) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return right;
    }
}