[LeetCode] 283. Move Zeroes 移动零

Posted 2020-10-26 轻风舞动

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.

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

把一个数组里所有的0都移到后面，不能改变非零数的相对位置关系，而且不能拷贝额外的数组。

要用替换法in-place，双指针来做，前面的指针指向处理过的最后一个非零数字， 后面一个指针向后扫，遇到非零数字，和前面指针所指数字交换位置，前面指针后移1位。

或者不交换只把非零的数字换到前面，最后子统一把后面的全部变成0。

Java: Time Complexity: O(n), Space Complixity: O(1)

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;
        }
    }
}

Python:

class Solution(object):
    def moveZeroes(self, nums):
        """
        :type nums: List[int]
        :rtype: void Do not return anything, modify nums in-place instead.
        """
        pos = 0
        for i in xrange(len(nums)):
            if nums[i]:
                nums[i], nums[pos] = nums[pos], nums[i]
                pos += 1

C++:

class Solution {
public:
    void moveZeroes(vector<int>& nums) {
        int pos = 0;
        for (auto& num : nums) {
            if (num) {
                swap(nums[pos++], num);
            }
        }
    }
};