[LeetCode] 88. Merge Sorted Array

题目链接：传送门

Description

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

Note:
You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2. The number of elements initialized in nums1 and nums2 are m and n respectively.

Solution

题意：

合并两个有序序列

思路：

一开始很直接的去合并...

class Solution {
public:
    void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
        vector<int> res;
        int i = 0, j = 0;
        while (i < m && j < n) {
            if (nums1[i] <= nums2[j])  res.push_back(nums1[i++]);
            else  res.push_back(nums2[j++]);
        }
        while (i < m)  res.push_back(nums1[i++]);
        while (j < n)  res.push_back(nums2[j++]);
        nums1 = res;
    }
};

然后发现其实从尾到头合并更方便...

class Solution {
public:
    void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
        int i = m - 1, j = n - 1, k = m + n - 1;
        while (i >= 0 || j >= 0) {
            if (i < 0)  nums1[k--] = nums2[j--];
            else if (j < 0)  nums1[k--] = nums1[i--];
            else  nums1[k--] = nums1[i] >= nums2[j] ? nums1[i--] : nums2[j--];
        }
    }
};