PAT (Advanced Level) Practice 1054 The Dominant Color（20分）【哈希】

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, 800×600), 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 $[0,2^{24})$. 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

题意

找出出现次数超过半数的数，保证存在且只有一个。

思路

使用map。

代码

#include <iostream>
#include <unordered_map>

using namespace std;

int main() {
    cin.tie(nullptr);
    cout.tie(nullptr);
    ios::sync_with_stdio(false);

    int n, m, t, half;
    cin >> n >> m;
    half = m * n / 2;

    unordered_map<int, int> mp;
    for (int i = 0; i < n * m; ++i) {
        cin >> t;
        if (++mp[t] > half) {
            cout << t;
            return 0;
        }
    }
}