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#3028 - Ant on the Boundary

Easy • View on LeetCode • View on GitHub

Array Prefix Sum Simulation

Problem Description

An ant is on a boundary. It sometimes goes left and sometimes right.

You are given an array of non-zero integers nums. The ant starts reading nums from the first element of it to its end. At each step, it moves according to the value of the current element:

If nums[i] < 0, it moves left by -nums[i] units.
If nums[i] > 0, it moves right by nums[i] units.

Return the number of times the ant returns to the boundary.

Notes:

There is an infinite space on both sides of the boundary.
We check whether the ant is on the boundary only after it has moved |nums[i]| units. In other words, if the ant crosses the boundary during its movement, it does not count.

Solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var returnToBoundaryCount = function(nums) {
  let position = 0;
  let result = 0;

  for (const step of nums) {
    position += step;
    if (position === 0) {
      result++;
    }
  }

  return result;
};