剑指offer双指针21.调整数组顺序使奇数位于偶数前面

Posted 2021-02-28 trevo

题目链接：https://leetcode-cn.com/problems/diao-zheng-shu-zu-shun-xu-shi-qi-shu-wei-yu-ou-shu-qian-mian-lcof/

双指针

class Solution {
public:
    vector<int> exchange(vector<int>& nums) {
        int i = 0;
        int j = nums.size() - 1;
        while(i < j)
        {
            if(nums[j] % 2 == 0)
                j--;
            else if(nums[i] % 2 == 1)
                i++;
            else
                swap(nums[i], nums[j]);
        }
        return nums;
    }
};

双指针 + 位运算

class Solution {
public:
    vector<int> exchange(vector<int>& nums) {
        int i = 0;
        int j = nums.size() - 1;
        while(i < j)
        {
            if((nums[j] & 1) != 1)
                j--;
            else if((nums[i] & 1) != 0)
                i++;
            else
                swap(nums[i], nums[j]);
        }
        return nums;
    }
};

快慢指针

与上面指针的初始指向不同，刚开始i=j=0;
   j为快指针，i为慢指针
   i用来记录下一个要交换偶数的位置
   j用来奇数

class Solution {
public:
    vector<int> exchange(vector<int>& nums) {
        int i = 0, j = 0;
        while (j < nums.size()) 
        {
            if (nums[j] & 1) //找奇数
            {
                swap(nums[i], nums[j]);
                i ++;
            }
            j ++;
        }
        return nums;
    }
};