number-of-subsequences-that-satisfy-the-given-sum-condition.py

# Time:  O(nlogn)
# Space: O(n)

class Solution(object):
    def numSubseq(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        MOD = 10**9 + 7
        nums.sort()
        result = 0
        left, right = 0, len(nums)-1
        while left <= right:
            if nums[left]+nums[right] > target:
                right -= 1
            else:
                result = (result+pow(2, right-left, MOD))%MOD
                left += 1
        return result