CodeForces - 1033A

Alice and Bob are playing chess on a huge chessboard with dimensions n×nn×n. Alice has a single piece left — a queen, located at (ax,ay)(ax,ay), while Bob has only the king standing at (bx,by)(bx,by). Alice thinks that as her queen is dominating the chessboard, victory is hers.

But Bob has made a devious plan to seize the victory for himself — he needs to march his king to (cx,cy)(cx,cy) in order to claim the victory for himself. As Alice is distracted by her sense of superiority, she no longer moves any pieces around, and it is only Bob who makes any turns.

Bob will win if he can move his king from (bx,by)(bx,by) to (cx,cy)(cx,cy) without ever getting in check. Remember that a king can move to any of the 88 adjacent squares. A king is in check if it is on the same rank (i.e. row), file (i.e. column), or diagonal as the enemy queen.

Find whether Bob can win or not.

Input
The first line contains a single integer nn (3≤n≤1000) — the dimensions of the chessboard.

The second line contains two integers axax and ayay (1≤ax,ay≤n1≤ax,ay≤n) — the coordinates of Alice's queen.

The third line contains two integers bxbx and byby (1≤bx,by≤n1≤bx,by≤n) — the coordinates of Bob's king.

The fourth line contains two integers cxcx and cycy (1≤cx,cy≤n1≤cx,cy≤n) — the coordinates of the location that Bob wants to get to.

It is guaranteed that Bob's king is currently not in check and the target location is not in check either.

Furthermore, the king is not located on the same square as the queen (i.e. ax≠bxax≠bx or ay≠byay≠by), and the target does coincide neither with the queen's position (i.e. cx≠axcx≠ax or cy≠aycy≠ay) nor with the king's position (i.e. cx≠bxcx≠bx or cy≠bycy≠by).

Output
Print "YES" (without quotes) if Bob can get from (bx,by)(bx,by) to (cx,cy)(cx,cy) without ever getting in check, otherwise print "NO".

You can print each letter in any case (upper or lower).

Examples
Input
8
4 4
1 3
3 1
Output
YES
Input
8
4 4
2 3
1 6
Output
NO
Input
8
3 5
1 2
6 1
Output
NO

解题思路：由题意可知女王(ax,ay)所在的那一行和那一列国王(bx,by)都不能通过.这样我们就可以令(ax,ay)为原点建立平面直角坐标系，国王(bx,by)只能在其所在的象限移动，所以我们只需判断(bx,by)和(cx,cy)是否在同一象限即可。

include<stdio.h>

int main()
{
int n,xb,xc,yb,yc,y,ax,bx,cx,ay,by,cy;
while(~scanf("%d",&n))
{
scanf("%d%d%d%d%d%d",&ax,&ay,&bx,&by,&cx,&cy);
xb=bx-ax;yb=by-ay;//(xb,yb)代表以(ax,ay)为原点(bx,by)所在的位置
xc=cx-ax;yc=cy-ay;//同上
if(xb>0&&xc>0&yb>0&&yc>0||xb<0&&xc<0&&yb>0&&yc>0||xb<0&&xc<0&&yb<0&&yc<0||xb>0&&xc>0&&yb<0&&yc<0)//判断(xb,yb)和(xc,yc)是否在同一象限
printf("YES\n");
else
printf("NO\n");
}
}