兩個有序數組，求第K小數

<pre name="code" class="cpp">兩個有序數組A[0...m-1],B[0...n-1]，A與B中所有元素均不重複，求A[],B[]合成數組的第K小數

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;
    }
};