A1117. Eddington Number

British astronomer Eddington liked to ride a bike. It is said that in order to show off his skill, he has even defined an "Eddington number", E -- that is, the maximum integer E such that it is for E days that one rides more than E miles. Eddington's own E was 87.

Now given everyday's distances that one rides for N days, you are supposed to find the corresponding E (<=N).

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N(<=105), the days of continuous riding. Then N non-negative integers are given in the next line, being the riding distances of everyday.

Output Specification:

For each case, print in a line the Eddington number for these N days.

Sample Input:

10
6 7 6 9 3 10 8 2 7 8

Sample Output:

6
 #include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
int N, num[];
bool cmp(int a, int b){
return a > b;
}
int main(){
int E;
scanf("%d", &N);
for(int i = ; i <= N; i++){
scanf("%d", &num[i]);
}
sort(num + , num + N + , cmp);
E = N;
for(int i = ; i <= N; i++){
if(i >= num[i]){
E = i - ;
break;
}
} printf("%d", E);
cin >> N;
return ;
}

总结:

1、题意:给出N个数,求一个最大的m,使得有m个数大于m。

2、找规律可以发现,先对序列递减排序后,只要 i 大于 num[ i ],则 i - 1也会大于 num[ i - 1](i之前的都满足,这里i从1开始)。这样只要找到一个 i 小于等于 num[ i ],则说i - 1即为所求。

3、要注意遍历完整个序列结果都满足的情况,需要将E 初始化为N。(N = 3, 序列为 4   4   4)

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