いろはちゃんとマス目 / Iroha and a Grid AtCoder - 1974 45分钟AK赛

Problem Statement

 

We have a large square grid with H rows and W columns. Iroha is now standing in the top-left cell. She will repeat going right or down to the adjacent cell, until she reaches the bottom-right cell.

However, she cannot enter the cells in the intersection of the bottom A rows and the leftmost B columns. (That is, there are A×B forbidden cells.) There is no restriction on entering the other cells.

Find the number of ways she can travel to the bottom-right cell.

Since this number can be extremely large, print the number modulo 10⁹+7.

Constraints

 

• 1≦H,W≦100,000
• 1≦A<H
• 1≦B<W

Input

 

The input is given from Standard Input in the following format:

H W A B

Output

 

Print the number of ways she can travel to the bottom-right cell, modulo 10⁹+7.

Sample Input 1

 

2 3 1 1

Sample Output 1

 

2

We have a 2×3 grid, but entering the bottom-left cell is forbidden. The number of ways to travel is two: "Right, Right, Down" and "Right, Down, Right".

Sample Input 2

 

10 7 3 4

Sample Output 2

 

3570

There are 12 forbidden cells.

Sample Input 3

 

100000 100000 99999 99999

Sample Output 3

 

1

Sample Input 4

 

100000 100000 44444 55555

Sample Output 4

 

738162020

//44m36sAK！！！
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转载于:https://www.cnblogs.com/upstart/p/8982402.html