88. Merge Sorted Array

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

Note:

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

Input:
nums1 = [1,2,3,0,0,0], m = 3
nums2 = [2,5,6],       n = 3

Output: [1,2,2,3,5,6]

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/merge-sorted-array
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合并两个有序数组。

对两个有序数组，分别设置一个指针，都从有数字的位置开始，从后往前遍历。大的数组就先放在相应的位置。

class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        int len = m + n;
        int index1 = m - 1;
        int index2 = n - 1;
        // 从后往前放
        for (int i = len - 1; i >= 0; i--) {
            // 如果nums2遍历完了，直接放回
            if (index2 < 0)
                break;
            // nums1 遍历完了，把nums2剩下的都放进去
            if (index1 < 0) {
                nums1[i] = nums2[index2];
                index2--;
                continue;
            }
            // 放二者较大的数字在nums1中
            if (nums1[index1] <=  nums2[index2]) {
                nums1[i] = nums2[index2];
                index2--;
            } else {
                nums1[i] = nums1[index1];
                index1--;
            }
        }
    }
}