leetcode解题: Move Zeros (283)

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

解法1：双指针 O(N) time with O(1) space

这题的思路很像Quick Sort里partition的思路，需要用到两个指针。一个指针用来traverse，另一个用来记录下一个非0的元素需要插入的位置。
C++中有一个swap function，可以交换两个reference的值。
C++

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class Solution {
public:
    void moveZeroes(vector<int>& nums) {
        if (nums.size() == 0) {
            return;
        }
        for (int i = 0, j = 0; i < nums.size(); i++) {
            if (nums[i]) {
                swap(nums[i], nums[j++]);
            }
        }
    }
};

Java

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