LeetCode----Median of Two Sorted Arrays

Median of Two Sorted Arrays

 

There are two sorted arrays A and B of size m and n respectively. Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)).

分析：

这是一题经典的题。其一般形式是 在两个已排序数组中寻找第 K 大的数。

通过 比较两个数组中 A[k/2-1] 和 B[k/2-1的大小，可以每次将规模从 k 减少到 K/2.

class Solution {
public:
    double findMedianSortedArrays(int A[], int m, int B[], int n) {
        int len(m+n);
        if(len & 0x1)
          return findKthSortedArrays(A, m, B, n, len/2+1);
        else
          return (findKthSortedArrays(A, m, B, n, len/2) + findKthSortedArrays(A, m, B, n, len/2+1)) / 2.0;
    }
private:
    double findKthSortedArrays(int A[], int m, int B[], int n, int k)
    {
        //assume m >= n
        if(m < n) return findKthSortedArrays(B, n, A, m, k);
        if(n == 0) return A[k-1];
        if(k == 1) return min(A[0], B[0]);
        
        int pb = min(n, k/2);
        int pa = k - pb;
        if(A[pa-1] == B[pb-1]) return A[pa-1];
        else if(A[pa-1] < B[pb-1]) return findKthSortedArrays(A+pa, m-pa, B, n, k-pa);
        else return findKthSortedArrays(A, m, B+pb, n-pb, k-pb);
    }
};