程序碎片- 矩阵乘法优化(dp,循环)

下班了换个eclipse写写，感觉还蛮好的。

这个循环的原理是，沿着矩阵的对角线，一层层向上计算，

发现这样的过程中，前面的条件都已经算好了。所以就不用递归了。

import java.util.ArrayList;

 

public class MatrixMultiply {

    public MatrixMultiply() {

       Matrix m1 = new Matrix(2, 5);

       Matrix m2 = new Matrix(5, 100);

       Matrix m3 = new Matrix(100, 4);

       Matrix m4 = new Matrix(4, 50);

       Matrix m5 = new Matrix(50, 6);

       MList.add(m1);

       MList.add(m2);

       MList.add(m3);

       MList.add(m4);

       MList.add(m5);

       for (int i = 0; i < 5; i++)

           for (int j = 0; j < 5; j++) {

              if (i >= j)

                  M[i][j] = 0;

              else

                  M[i][j] = Integer.MAX_VALUE;

           }

    }

 

    private int[][] M = new int[5][5];

    private ArrayList<Matrix> MList = new ArrayList<Matrix>();

 

    public void getResult() {

       // already fill the left-below half of the matrix, now fill the left-up

       // part, the specialIndex is build by analysis matrix's structure

       for (int specialIndex = 1; specialIndex < 5; specialIndex++) {

           int xIndex = 0;

           int yIndex = xIndex + specialIndex;

           while (yIndex < 5) {

              M[xIndex][yIndex] = getMax(xIndex, yIndex);

              yIndex++;

              xIndex++;

           }

       }

       System.out.println("the optimized result is :" + M[0][4]);

    }

 

    private int getMax(int xIndex, int yIndex) {

       if (M[xIndex][yIndex] != Integer.MAX_VALUE)

           return M[xIndex][yIndex];

       else {

           int finalMin = Integer.MAX_VALUE;

           int tempMin;

           for (int k = xIndex; k < yIndex; k++) {

              tempMin = M[xIndex][k] + M[k + 1][yIndex]

                     + MList.get(xIndex).orderX * MList.get(k).orderY

                     * MList.get(yIndex).orderY;

              if (finalMin > tempMin)

                  finalMin = tempMin;

           }

           return finalMin;

       }

    }

 

    class Matrix {

       public Matrix(int x, int y) {

           orderX = x;

           orderY = y;

       }

 

       int orderX;

       int orderY;

    }

 

}