程序员面试金典 - 面试题 05.08. 绘制直线（位运算）

示例1:
 输入：length = 1, w = 32, x1 = 30, x2 = 31, y = 0
 输出：[3]
 说明：在第0行的第30位到第31为画一条直线，屏幕表示为[0b000000000000000000000000000000011]
 
示例2:
 输入：length = 3, w = 96, x1 = 0, x2 = 95, y = 0
 输出：[-1, -1, -1]

class Solution {
public:
    vector<int> drawLine(int length, int w, int x1, int x2, int y) {
        int n = w>>5, idx = y*n;
        vector<int> ans(length,0);
        while(x1 > 31)//不在当前int内
        {
        	idx++;//下一个int
        	x1 -= 32;//区间挪动
        	x2 -= 32;
        }
        int l = x1, r;//找到了x1所在int
        for( ; x2>=0; l=0,x2-=32)
        {
        	r = min(x2,31);//右端点
        	for(int i = l; i <= r; i++)
        	{
        		ans[idx] |= 1<<(31-i);//把1挪到各个位置上
        	}
        	idx++;
        }
        return ans;
    }
};