Rectangular footprint (dp) Algorithm

problem

We can use 2 small rectangle 1 of sideways or vertically to cover a larger rectangle.
Will the use of n 2 small rectangle 1 coverage without overlap a large rectangle 2 * n, the
total number of ways?

analysis

这种问题上来找不到规律，是啥啊？
Can first draw a few pictures, look for the law?
就相当于解数学题，肯定是有什么规律的？

• n=1 Case 1
• n=2 Case 2

• ·n=3
  
• n=4
  
  To summarize the above rules, can be found n pendulum method and d of the two front n-1and n-2related pendulum method, i.e.F(n)=F(n-1)+F(n-2)

This is the meager number of columns ah concubinage

Code implementation (recursive version)

  public int RectCover(int target) {

        if(target<1)
            return 0;
        if(target==1){
            return 1;
        }
        if(target==2){
            return 2;
        }

        return RectCover(target-1)+RectCover(target-2);

    }

Code implementation (loop version)

 public int RectCover2(int target){

        if(target<1){
            return 0;
        }

        if(target==1){
            return 1;
        }

        if(target==2){
            return 2;
        }

        int preNum = 2;
        int prepreNum = 1;
        int result = 0;
        for(int i=3;i<=target;i++){
            result = preNum+prepreNum;
            prepreNum=preNum;
            preNum=result;
        }
        return result;
    }