期末預測之最佳閾值

#include<bits/stdc++.h>
using namespace std;

struct node {
    int y,result;
};
vector<node> nodes;

bool cmp(node &a,node &b) {
    if(a.y != b.y) return a.y < b.y;
    else return a.result < b.result;
}
vector<long int> cnt_0,cnt_1;
int main() {
    int m,y,result;
    scanf("%d",&m);
    for(int i = 0 ; i < m; ++i) {
        scanf("%d%d",&y,&result);
        nodes.push_back({y,result});
    }
    sort(nodes.begin(),nodes.end(),cmp); //先對輸入排序
    
    //cnt_0存儲y前面result為0的個數
    //cnt_1存儲y前面result為1的個數 
    cnt_0.resize(m);
    cnt_1.resize(m);
    if(nodes[0].result == 0) {
        cnt_0[0] = 1;
        cnt_1[0] = 0;
    } else {
        cnt_0[0] = 0;
        cnt_1[0] = 1;
    }
    for(int i = 1; i < nodes.size(); ++i) {
        if(nodes[i].result == 0) {
            cnt_0[i] = cnt_0[i-1] + 1;
            cnt_1[i] = cnt_1[i-1];
        } else {
            cnt_1[i] = cnt_1[i-1] + 1;
            cnt_0[i] = cnt_0[i-1];
        }
    }

    // 初始化
    int final_y = nodes[0].y;
    long int final_cnt = cnt_1[m-1];

    for(int i = 1; i < m; ++i) {
        long int current_cnt = 0;
        while(nodes[i].y == nodes[i-1].y && i < m) //如果前面計算過y，則跳過 
            ++i;
        current_cnt = cnt_0[i-1] + cnt_1[m-1] - cnt_1[i-1]; //y的正確預測次數 = y前面result為0的個數 +  y以及y后面result為1的個數 
        if(current_cnt >= final_cnt) {
            final_cnt = current_cnt;
            final_y = nodes[i].y;
        }
    }
    printf("%d",final_y);
    return 0;
}