• [1429] Annoying Painting Tool

  • 时间限制: 1000 ms 内存限制: 65535 K
  • 问题描述
  • Maybe you wonder what an annoying painting tool is? First of all, the painting tool we speak of supports only black and white. Therefore, a picture consists of a rectangular area of pixels, which are either black or white. Second, there is only one operation how to change the colour of pixels:

    Select a rectangular area of r rows and c columns of pixels, which is completely inside the picture. As a result of the operation, each pixel inside the selected rectangle changes its colour (from black to white, or from white to black).

    Initially, all pixels are white. To create a picture, the operation described above can be applied several times. Can you paint a certain picture which you have in mind?


  • 输入
  • The input contains several test cases. Each test case starts with one line containing four integers n, m, r and c. (1 ≤ r ≤ n ≤ 100, 1 ≤ c ≤ m ≤ 100), The following n lines each describe one row of pixels of the painting you want to create. The ith line consists of m characters describing the desired pixel values of the ith row in the finished painting ('0' indicates white, '1' indicates black).

    The last test case is followed by a line containing four zeros.
  • 输出
  • For each test case, print the minimum number of operations needed to create the painting, or -1 if it is impossible.
  • 样例输入
  • 3 3 1 1
    010
    101
    010
    4 3 2 1
    011
    110
    011
    110
    3 4 2 2
    0110
    0111
    0000
    0 0 0 0
    
  • 样例输出
  • 4
    6
    -1
    
  • 提示
  • 来源
  • Hungar
  • 操作

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