0027. Remove Element.js

// Given an array nums and a value val, remove all instances of that value in-place and return the new length.

// Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

// The order of elements can be changed. It doesn't matter what you leave beyond the new length.

// Example 1:

// Given nums = [3,2,2,3], val = 3,

// Your function should return length = 2, with the first two elements of nums being 2.

// It doesn't matter what you leave beyond the returned length.

// Example 2:

// Given nums = [0,1,2,2,3,0,4,2], val = 2,

// Your function should return length = 5, with the first five elements of nums containing 0, 1, 3, 0, and 4.

// Note that the order of those five elements can be arbitrary.

// It doesn't matter what values are set beyond the returned length.

// Clarification:

// Confused why the returned value is an integer but your answer is an array?

// Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.

// Internally you can think of this:

// // nums is passed in by reference. (i.e., without making a copy)
// int len = removeElement(nums, val);

// // any modification to nums in your function would be known by the caller.
// // using the length returned by your function, it prints the first len elements.
// for (int i = 0; i < len; i++) {
//     print(nums[i]);
// }


// 1) 双指针
/**
 * @param {number[]} nums
 * @param {number} val
 * @return {number}
 */
var removeElement = function(nums, val) {
  let i = 0;
  let j = 0;
  while (j < nums.length) {
    if (nums[j] !== val) {
      nums[i] = nums[j];
      i++;
    }
    j++;
  }
  return i;
};
// Runtime: 68 ms, faster than 10.72% of JavaScript online submissions for Remove Element.
// Memory Usage: 33.9 MB, less than 16.67% of JavaScript online submissions for Remove Element.


// 2) 双指针-要删除的元素稀少
/**
 * @param {number[]} nums
 * @param {number} val
 * @return {number}
 */
var removeElement = function(nums, val) {
  let i = 0
  let j = nums.length
  while (i < j) {
    if (nums[i] == val) {
      nums[i] = nums[j - 1]
      j--
    } else {
      i++
    }
  }
  return i
};
// Runtime: 56 ms, faster than 63.49% of JavaScript online submissions for Remove Element.
// Memory Usage: 33.9 MB, less than 16.67% of JavaScript online submissions for Remove Element.