CF95B Lucky Numbers [毒瘤分类讨论贪心/DFS]
其实代码用不着这么多goto,不过写着方便~
详细分析有时间再写吧
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73
| #include <iostream> #include <algorithm> #include <cstring> #include <cstdio> using namespace std;
const int MAXN = 1e5+10;
char a[MAXN],ans[MAXN]; int n;
int main(){ cin >> (a+1); int n = strlen(a+1); if(n & 1){ ODD_N: for(int i = 1;i<=n/2 + 1;i++){ putchar('4'); } for(int i = 1;i<=n/2 + 1;i++){ putchar('7'); } putchar('\n'); }else{ int lead4 = 0,lead7 = 0,now = 1; while(now <= n){ if(a[now] < '4'){ break; }else if(a[now] == '4' && lead4 < n/2){ ans[now] = '4'; lead4++; now++; }else if(a[now] < '7' && lead7 < n/2){ ans[now] = '7'; lead7++; break; }else if(a[now] == '7' && lead7 < n/2){ ans[now] = '7'; lead7++; now++; }else{ goto TRY_LAST_USE_7; } } if(false){ TRY_LAST_USE_7: while(--now){ if(ans[now] == '4'){ lead4--; }else{ lead7--; } if(ans[now] < '7' && lead7 < n/2){ ans[now] = '7'; lead7++; goto OUTPUT; } } goto ODD_N; } OUTPUT: for(int i = 1;i<=lead4 + lead7;i++){ putchar(ans[i]); } for(int i = 1;i<=n/2 - lead4;i++){ putchar('4'); } for(int i = 1;i<=n/2 - lead7;i++){ putchar('7'); } putchar('\n'); } }
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