两个有序数组，求第K小数

<pre name="code" class="cpp">两个有序数组A[0...m-1],B[0...n-1]，A与B中所有元素均不重复，求A[],B[]合成数组的第K小数

class Solution {
public:
//there are no duplicate elements in array A or B.
int findKthSmallest(int A[], int m, int B[], int n, int k) {
assert(k > 0 && k <= m + n);
assert(m >= 0 && n >= 0);

int i = (m + 0.0) / (m + n) * (k - 1); //i=m/(m+n)*(k-1)
int j = k - 1 - i; // i+j=k-1 >>> j = (k-1)-i = (k-1)-[m/(m+n)*(k-1)] = n/(m+n)*(k-1)

assert(i >= 0 && i <= m);
assert(j >= 0 && j <= n);

int Ai = (i == m ? INT_MAX : A[i]);
int Ai_1 = (i == 0 ? INT_MIN : A[i-1]);
int Bj = (j == n ? INT_MAX : B[j]);
int Bj_1 = (j == 0 ? INT_MIN : B[j-1]);
if(Ai_1 < Bj && Bj < Ai) return Bj;
if(Bj_1 < Ai && Ai < Bj) return Ai;

assert((Ai > Bj && Ai_1 > Bj) || (Bj > Ai && Bj_1 > Ai));

if(Bj < Ai) return findKthSmallest(A, i, B + j + 1, n - j - 1, k - j - 1);
if(Ai < Bj) return findKthSmallest(A + i + 1, m - i - 1, B, j, k - i - 1);
return -1;
}
};