[Leetcode 31] 88 Merge Sorted Array

Problem:

Given two sorted integer arrays A and B, merge B into A as one sorted array.

Note:
You may assume that A has enough space to hold additional elements from B. The number of elements initialized in A and B are m and n respectively.

Analysis:

To finish the task efficiently, merge should started from the end of the two arrays.

Note, we can compute the total length of the new array by add A and B's separate length. Also remember to update the index of next elements to be merged

The time complexity is O(n+m), space complexity is O(n+m).

Code:

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int totalLen = m + n, aLast = m-1, bLast = n-1;
        
        for (int i=m+n-1; i>=0; i--) {
            if (aLast < 0)  
                A[i] = B[bLast--];
            else if (bLast < 0)  
                A[i] = A[aLast--];
            else
                A[i] = (A[aLast] > B[bLast])?A[aLast--] : B[bLast--];
        }
    }
};

Attention: