算法笔记练习 4.2 散列 问题 C: 【PAT A1041】Be Unique

算法笔记练习 题解合集

题目链接

题目

题目描述
Being unique is so important to people on Mars that even their lottery is designed in a unique way. The rule of winning is simple: one bets on a number chosen from [1, 104]. The first one who bets on a unique number wins. For example, if there are 7 people betting on 5 31 5 88 67 88 17, then the second one who bets on 31 wins.

输入
Each input file contains one test case. Each case contains a line which begins with a positive integer N (<=105) and then followed by N bets. The numbers are separated by a space.

输出
For each test case, print the winning number in a line. If there is no winner, print “None” instead.

样例输入
7 5 31 5 88 67 88 17
5 888 666 666 888 888

样例输出
31
None

思路

1. 用 inputs 接收所有输入，同时用 cnt 数组统计所有数字的出现次数（cnt[i] 表示数字 i 出现的次数）
2. 遍历 inputs，在 cnt 中检查每个数的出现次数，若存在出现次数为 1 的数，立即输出，若没有找到，输出 None

代码

#include <stdio.h>
#define MAX 100010
int main(){
	int N, i;
	while (scanf("%d", &N) != EOF){
		int inputs[N]; 
		int cnt[MAX] = {0};
		// 接收所有数字，并用 cnt 统计出现次数
		for (i = 0; i < N; ++i){
			scanf("%d", &inputs[i]);
			++cnt[inputs[i]];
		}
		// 遍历 inputs，若存在出现次数为 1 的数，立即输出
		for (i = 0; i < N; ++i){
			if (cnt[inputs[i]] == 1){
				printf("%d\n", inputs[i]);
				break;
			} 
		}
		// 没找到
		if (i == N)
			printf("None\n");
	} 
	return 0;
}