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数轴上有 n条线段，选取其中 k条线段使得这 k条线段两两没有重合部分，问最大的k为多少?

输入

输入文件segment.in的第一行为一个正整数 n；下面 n行每行有 2个数字ai,bi，描述每条线段。

输出

输出文件segment.out仅包括一个整数，为k的最大值。

样例输入

3
0 2
2 4 
1 3

样例输出

2

C语言代码

#include <stdio.h>
#include <stdlib.h>

// 定义结构体来存储一组数据的两个属性
struct Data {
    int first;
    int second;
};

// 比较函数，用于qsort进行结构体数组按照second成员升序排序
int compare(const void *a, const void *b) {
    struct Data *x = (struct Data *)a;
    struct Data *y = (struct Data *)b;
    return x->second - y->second;
}

int main() {
    int num;
    scanf(“%d”, &num);
    struct Data *dataArr = (struct Data *)malloc(num * sizeof(struct Data));
    if (dataArr == NULL) {
        printf(“内存分配失败\n”);
        return -1;
    }
    // 循环读取每组数据的两个属性值
    for (int i = 0; i < num; i++) {
        scanf(“%d %d”, &dataArr[i].first, &dataArr[i].second);
    }

    // 使用qsort对结构体数组进行排序
    qsort(dataArr, num, sizeof(struct Data), compare);

    int count = 1;
    int prevSecond = dataArr[0].second;
    for (int i = 1; i < num; i++) {
        if (prevSecond <= dataArr[i].first) {
            prevSecond = dataArr[i].second;
            count++;
        }
    }

    printf(“%d\n”, count);

    free(dataArr);
    return 0;
}

Java代码

import java.util.Arrays;
import java.util.Scanner;

class Data {
    int first;
    int second;

    public Data(int first, int second) {
        this.first = first;
        this.second = second;
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int numElements = scanner.nextInt();
        Data[] dataArray = new Data[numElements];
        for (int i = 0; i < numElements; i++) {
            int f = scanner.nextInt();
            int s = scanner.nextInt();
            dataArray[i] = new Data(f, s);
        }

        Arrays.sort(dataArray, (x, y) -> x.second - y.second);

        int count = 1;
        int prevSecond = dataArray[0].second;
        for (int i = 1; i < numElements; i++) {
            if (prevSecond <= dataArray[i].first) {
                prevSecond = dataArray[i].second;
                count++;
            }
        }

        System.out.println(count);
    }
}

C++代码

#include <iostream>
#include <algorithm>
using namespace std;

struct Data {
    int first;
    int second;
};

// 比较函数，用于按照结构体中second成员升序排序
bool compare(Data x, Data y) {
    return x.second < y.second;
}

int main() {
    int num;
    cin >> num;
    Data dataArr[num];
    for (int i = 0; i < num; i++) {
        cin >> dataArr[i].first >> dataArr[i].second;
    }

    sort(dataArr, dataArr + num, compare);

    int result = 1;
    int prevSecond = dataArr[0].second;
    for (int i = 1; i < num; i++) {
        if (prevSecond <= dataArr[i].first) {
            prevSecond = dataArr[i].second;
            result++;
        }
    }

    cout << result << endl;
    return 0;
}

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