程序员面试金典 - 面试题 16.06. 最小差（排序+双指针）

示例：
输入：{1, 3, 15, 11, 2}, {23, 127, 235, 19, 8}
输出： 3，即数值对(11, 8)

提示：
1 <= a.length, b.length <= 100000
-2147483648 <= a[i], b[i] <= 2147483647
正确结果在区间[-2147483648, 2147483647]内

class Solution {
public:
    int smallestDifference(vector<int>& a, vector<int>& b) {
    	sort(a.begin(), a.end());
    	sort(b.begin(), b.end());
    	if(a.back() <= b.front())
    		return b.front()-a.back();
    	if(b.back() <= a.front())
    		return a.front()-b.back();
    	int i = 0, j = 0, na = a.size(), nb = b.size(),mindis = INT_MAX;
        long diff;
    	while(i < na && j < nb)
    	{
            diff = a[i]-b[j];
            if(diff <= INT_MAX && diff > INT_MIN) 
                mindis = min(mindis, abs((int)diff));
    		if(a[i] <= b[j])
    			i++;//a小，a往后走，找大的，缩小差距
    		else
    			j++;//b小，b往后找大的
    	}
    	return mindis;
    }
};