【找规律】HDOJ Rikka with Chess 5630

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在n×m的黑白相间棋盘上，每次选择一个矩形区域进行颜色反转，目标是将所有格子变为同一颜色。本文探讨如何通过算法找到达到此目标所需的最少反转次数。

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Rikka with Chess

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 351 Accepted Submission(s): 299

Problem Description

Yuta gives Rikka a chess board of size

n×m .

As we all know, on a chess board, every cell is either black or white and every two cells that share a side have different colors.

Rikka can choose any rectangle formed by board squares and perform an inversion, every white cell becomes black, and vice versa.

Rikka wants to turn all cells into the same color, please tell Rikka the minimal number of inversions she need to achieve her goal.

Input

The first line contains a number

T(T≤10) ——The number of the testcases.

Each testcase contains two numbers

n,m(n≤109,m≤109) .

Output

For each testcase, print a single number which represents the answer.

Sample Input

Sample Output

Source

BestCoder Round #73 (div.2)

题意：

一个 $\times m$ 的黑白相间的棋盘，每次可以选择一个矩形把其中的所有格子反色。问把所有格子变成一种颜色时的最少操作次数。

解题思路：

画几个图就能找到规律了，每次都是改变最小的行列的不同的。

AC代码：

#include <cstdio>
#include <algorithm>

using namespace std;

int main()
{
    int t;
    scanf("%d",&t);
    while(t--){
        int n,m;
        scanf("%d%d",&n,&m);
        printf("%d\n",m/2+n/2);
    }
    return 0;
}