刚刚交了一道题目，总结一下

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# include <stdio.h>

long int recaman[500001];int used[5000000] = {0};// if an integer is not used, the mark is 0 int main(void){long int i, k;long int m;for (i = 0; i < 500001; i++){if (i - 1 < 0){recaman[i] = 0;}else{m = recaman[i-1] - i;if (m > 0 && used[m] == 0)recaman[i] = m;elserecaman[i] = m + i + i;}used[recaman[i]] = 1;}while(scanf("%ld", &k) != EOF && k >= 0){printf("%ld\n", recaman[k]);}return 0;}

Recaman's SequenceTime Limit:1000ms, Special Time Limit:2500ms, Memory Limit:65536KBTotal submit users: 1183, Accepted users: 1023 Problem 10010 : No special judgement

Problem description

The Recaman's sequence is defined by a0 = 0 ; for m > 0, a_m = a_m−1 − m if the rsulting a_m is positive and not already in the sequence, otherwise a_m = a_m−1 + m.
The first few numbers in the Recaman's Sequence is 0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9 ...
Given k, your task is to calculate a_k.

The first few numbers in the Recaman's Sequence is 0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9 ...
Given k, your task is to calculate a_k.

Input

The input consists of several test cases. Each line of the input contains an integer k where 0 <= k <= 500000. The last line contains an integer −1, which should not be processed.

Output

For each k given in the input, print one line containing a_k to the output.

Sample Input

710000-1

Sample Output

if (m > 0 && used[m] == 0)

注意一点，C语言中有一个特点，就是逻辑与运算，千万不要把上面这条语句&&两边的调换过来，否则数组访问会出错！！

while(scanf("%ld", &k) != EOF && k >= 0)

另外还有一点，写代码时候千万要认真，刚才就是在上面这个语句后面加了分号，，，，，我结果后来才发现。