LeetCode ---- Merge Sorted Array

题目链接

Problem discription

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 (size that is greater or equal to m + n) to hold additional elements from B. The number of elements initialized in A and B are m and n respectively.

Accpted Code 1 ( use extra space)

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        // we use "ai" and "bi" to keep trace 
        // of array A[] and B[] respectively
        // "ci" holds the number of elements that 
        // has been merged
        int ai = 0, bi = 0, ci = 0;
        // create an extra vector of size n+m 
        // to keep the sorted array
        vector<int> C(n + m);
        while (ci < n + m) {
            // from small to large 
            if (ai < m && (bi >= n || A[ai] <= B[bi])) {
                C[ci++] = A[ai++];
            } else {
                C[ci++] = B[bi++];
            }
        }
        // copy the sorted array from C to A
        for (int i = 0; i < n+m; i++) A[i] = C[i];
    }
};

Accepted Code (without extra space) Clear & Simple

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        // we use "ai", "bi" to iterator A[] and B[] 
        // from the end respectively
        // since the size of A[] equal to or greater n+m
        // thus we can use inplace sort by filling A[]
        // from A[n+m-1] to A[0]
        int ai = m - 1, bi = n - 1, ci = n + m - 1;
        while (ci >= 0) {
            if (ai >= 0 && (bi < 0 || A[ai] >= B[bi])) {
                A[ci--] = A[ai--];
            } else {
                A[ci--] = B[bi--];
            }
        }
    }
};