27. Remove Element
Tags: ‘Array’, ‘Two Pointers’
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 ofnumscontaining0,1,3,0, 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]);
}
Solution
双指针two pointer，不同于2Sum夹逼，这里是快慢双指针 i指向目标array结束后一位，j快指针遍历。每当遇到符合条件的数，放到i 并且increment i
public int removeElement(int[] nums, int val) {
if (nums == null) return 0;
// i is slow runner, also length of result
int i = 0; //
for (int j = 0; j < nums.length; j++) {
if (nums[j] != val) { // if there is a match, do nothing
nums[i] = nums[j];
i++;
}
}
return i;
}