布线问题：如图1所示，印刷电路板将布线区域划分成n*m个方格。精确的电路布线问题要求确定连接方格a的中点到b的中点的最短布线方案。在布线时，电路只能沿直线或直角布线，如图1所示。为了避免线路相交，已经布线的方格做了封锁标记（如图1中阴影部分），其他线路不允许穿过被封锁的方格。-The wiring problem: as shown in Figure 1, the printed circuit board wiring area is divided into n* m Box. Accurate circuit wiring question asked to determine the midpoint connected to the grid a to b the midpoint of the shortest wiring. When wiring the circuit only along a straight line or at right angles to the wiring, shown in Figure 1 above. In order to avoid the lines intersect, the wiring box blockade mark (shaded in Figure 1), other lines are not allowed to pass through the box is blocked.