#1498 - Number of Subsequences That Satisfy the Given Sum Condition

Medium • View on LeetCode • View on GitHub

Array Sorting Binary Search Two Pointers

Problem Description

You are given an array of integers nums and an integer target.

Return the number of non-empty subsequences of nums such that the sum of the minimum and maximum element on it is less or equal to target. Since the answer may be too large, return it modulo 109 + 7.

Solution

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var numSubseq = function(nums, target) {
  const MOD = 1e9 + 7;
  const sortedNums = nums.sort((a, b) => a - b);
  const length = nums.length;
  let result = 0;
  const powers = new Array(length).fill(1);

  for (let i = 1; i < length; i++) {
    powers[i] = (powers[i - 1] * 2) % MOD;
  }

  let left = 0;
  let right = length - 1;

  while (left <= right) {
    if (sortedNums[left] + sortedNums[right] <= target) {
      result = (result + powers[right - left]) % MOD;
      left++;
    } else {
      right--;
    }
  }

  return result;
};