1054. The Dominant Color (20)

Behind the scenes in the computer's memory, color is always talked about as a series of 24 bits of information for each pixel. In an image, the color with the largest proportional area is called the dominant color. A strictly dominant color takes more than half of the total area. Now given an image of resolution M by N (for example, 800x600), you are supposed to point out the strictly dominant color.

Input Specification:

Each input file contains one test case. For each case, the first line contains 2 positive numbers: M (<=800) and N (<=600) which are the resolutions of the image. Then N lines follow, each contains M digital colors in the range [0, 2²⁴). It is guaranteed that the strictly dominant color exists for each input image. All the numbers in a line are separated by a space.

Output Specification:

For each test case, simply print the dominant color in a line.

Sample Input:

5 3
0 0 255 16777215 24
24 24 0 0 24
24 0 24 24 24

Sample Output:

24

解题思路：这题就是moore voting算法的题目，moore voting的思想就是，在n个数中求大于n/2个的数，这个的数有且只有一个，这个数的总个数减去其余的个数之和必大于零。定义变量key代表当前i个数之前最多的数值，定义count来计数和key相等的个数，当通过比较i+1后的数，如果和key相等则count++，如果不相等count--，当count为0时代表此时前面所遍历的数中肯定不含所求的数（个数多于n/2），此时更新key值。

#include<iostream>
#include<cstdio>
using namespace std;
int main(){
	int n,m;
	int count=0;
	int key=-1;
	cin>>m>>n;
	int len=m*n;
	for(int i=0;i<len;i++){
		int tmp;
		scanf("%d",&tmp);
		if(tmp!=key){
			if(count == 0){
				key=tmp;
			}else{
				count--;
			}	
		}
		else{
			count++;
		}
	}
	printf("%d\n",key);
	return 0;
}