283. Move Zeroes

Given an array nums, write a function to move all 0's to the end of it while maintaining the relative order of the non-zero elements.

For example, given nums = [0, 1, 0, 3, 12], after calling your function, nums should be [1, 3, 12, 0, 0].

Note:

1. You must do this in-place without making a copy of the array.
2. Minimize the total number of operations.

Solution:

The idea is to maintain a pointer index, which points to the position that can put the next valid number.

We go through the input array. If we find a valid number, we put it (or exchange) to the position where index points to. And increases index by 1, which means it now points to a new available position to put a valid number.



Code:

public class Solution {
    public void moveZeroes(int[] nums) {
        int index = 0;
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != 0) {
                nums[index++] = nums[i];
            }
        }
        for (int i = index; i < nums.length; i++) {
            nums[i] = 0;
        }
    }
}

public class Solution {
    public void moveZeroes(int[] nums) {
        int index = 0;
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != 0) {
                int tmp = nums[i];
                nums[i] = nums[index];
                nums[index++] = tmp;
            }
        }
    }
}

public class Solution {
    public void moveZeroes(int[] nums) {
        int i = 0;
        for (int n : nums) {
            if (n != 0) {
                nums[i++] = n;
            }
        }
        while (i < nums.length) {
            nums[i++] = 0;
        }
    }
}