Leetcode 4. 两个排序数组的中位数

编写一个寻找第k个值的函数，然后……

class Solution {
public:
   int _find(vector<int>& a, int al, vector<int>& b, int bl,int k) {
    if (a.size() - al > b.size() - bl) return _find(b, bl, a, al, k);
    if (al == a.size()) return b[bl + k - 1];
    if (k == 1) return min(a[al], b[bl]);

    int an = min(k / 2, (int)a.size() - al), bn = k - an;
    if (a[al + an - 1] < b[bl + bn - 1]) return _find(a, al + an, b, bl, k - an);
    if (a[al + an - 1] == b[bl + bn - 1]) return a[al + an - 1];
    if (a[al + an - 1] > b[bl + bn - 1]) return _find(a, al, b, bl + bn, k - bn);
}
double findMedianSortedArrays(vector<int>& nums1, vector<int>& nums2) {
    double ans = 0.0;
    int k = nums1.size() + nums2.size();
    if (k & 1) return 1.0*_find(nums1, 0, nums2, 0,k / 2 + 1);
    else return (_find(nums1, 0, nums2, 0, k / 2) + _find(nums1, 0, nums2, 0, k / 2 + 1)) /2.0;
}
};