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]

Thoughts:

1. To fill the nums1 in place, should fill the array backwards: start with the last on both arrays and fill the larger one between nums[i] and nums[j]

2. Code

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

Alternate version:

class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        int i = m - 1, j = n - 1, merge = m + n - 1;
        // System.out.println("i: " + i + " j: " + j);
        while(i >= 0 && j >=0){
            nums1[merge--] = nums1[i] > nums2[j]?nums1[i--]:nums2[j--];
        }
        if (i< 0){
            // fill j
            while(j>=0) nums1[merge--] = nums2[j--];
        }
        if (j < 0){
            //fill i
            while(i>=0) nums1[merge--] = nums1[i--];
        }
        return;
    }
}