AtCoder ABC 140D Face Produces Unhappiness
题目链接:https://atcoder.jp/contests/abc140/tasks/abc140_d
题目大意
有一对 N 个人, 用字符串 S 表示, S[i] 如果等于 'L' 说明这个人面朝左, 如果等于 'R' 说明这个人面朝右, 如果一个人朝向的方向有另一个人的后背, 这个人就提供 1 点满意度, 现在你最多能进行如下操作 K 次(也可不执行):
- 将[L, R]区间内的人区间整体旋转180度, 当然他们的朝向也会随之改变.
问所能得到的最大满意度为多少?
分析
贪心, 每次旋转只能影响区间两端人的不高兴度,也就是每次旋转最多能让满意度加 2, 而只要有不满意的人, 我们就能找到这样的区间, 让满意度加 2, 所以答案就是min(初始满意度 + 2 * K, N - 1)
代码如下
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 #define INIT() ios::sync_with_stdio(false);cin.tie(0);cout.tie(0); 5 #define Rep(i,n) for (int i = 0; i < (n); ++i) 6 #define For(i,s,t) for (int i = (s); i <= (t); ++i) 7 #define rFor(i,t,s) for (int i = (t); i >= (s); --i) 8 #define ForLL(i, s, t) for (LL i = LL(s); i <= LL(t); ++i) 9 #define rForLL(i, t, s) for (LL i = LL(t); i >= LL(s); --i) 10 #define foreach(i,c) for (__typeof(c.begin()) i = c.begin(); i != c.end(); ++i) 11 #define rforeach(i,c) for (__typeof(c.rbegin()) i = c.rbegin(); i != c.rend(); ++i) 12 13 #define pr(x) cout << #x << " = " << x << " " 14 #define prln(x) cout << #x << " = " << x << endl 15 16 #define LOWBIT(x) ((x)&(-x)) 17 18 #define ALL(x) x.begin(),x.end() 19 #define INS(x) inserter(x,x.begin()) 20 #define UNIQUE(x) x.erase(unique(x.begin(), x.end()), x.end()) 21 #define REMOVE(x, c) x.erase(remove(x.begin(), x.end(), c), x.end()); // ?? x ?????? c 22 #define TOLOWER(x) transform(x.begin(), x.end(), x.begin(),::tolower); 23 #define TOUPPER(x) transform(x.begin(), x.end(), x.begin(),::toupper); 24 25 #define ms0(a) memset(a,0,sizeof(a)) 26 #define msI(a) memset(a,inf,sizeof(a)) 27 #define msM(a) memset(a,-1,sizeof(a)) 28 29 #define MP make_pair 30 #define PB push_back 31 #define ft first 32 #define sd second 33 34 template<typename T1, typename T2> 35 istream &operator>>(istream &in, pair<T1, T2> &p) { 36 in >> p.first >> p.second; 37 return in; 38 } 39 40 template<typename T> 41 istream &operator>>(istream &in, vector<T> &v) { 42 for (auto &x: v) 43 in >> x; 44 return in; 45 } 46 47 template<typename T> 48 ostream &operator<<(ostream &out, vector<T> &v) { 49 Rep(i, v.size()) out << v[i] << " \n"[i == v.size()]; 50 return out; 51 } 52 53 template<typename T1, typename T2> 54 ostream &operator<<(ostream &out, const std::pair<T1, T2> &p) { 55 out << "[" << p.first << ", " << p.second << "]" << "\n"; 56 return out; 57 } 58 59 inline int gc(){ 60 static const int BUF = 1e7; 61 static char buf[BUF], *bg = buf + BUF, *ed = bg; 62 63 if(bg == ed) fread(bg = buf, 1, BUF, stdin); 64 return *bg++; 65 } 66 67 inline int ri(){ 68 int x = 0, f = 1, c = gc(); 69 for(; c<48||c>57; f = c=='-'?-1:f, c=gc()); 70 for(; c>47&&c<58; x = x*10 + c - 48, c=gc()); 71 return x*f; 72 } 73 74 template<class T> 75 inline string toString(T x) { 76 ostringstream sout; 77 sout << x; 78 return sout.str(); 79 } 80 81 inline int toInt(string s) { 82 int v; 83 istringstream sin(s); 84 sin >> v; 85 return v; 86 } 87 88 //min <= aim <= max 89 template<typename T> 90 inline bool BETWEEN(const T aim, const T min, const T max) { 91 return min <= aim && aim <= max; 92 } 93 94 typedef long long LL; 95 typedef unsigned long long uLL; 96 typedef pair< double, double > PDD; 97 typedef pair< int, int > PII; 98 typedef pair< int, PII > PIPII; 99 typedef pair< string, int > PSI; 100 typedef pair< int, PSI > PIPSI; 101 typedef set< int > SI; 102 typedef set< PII > SPII; 103 typedef vector< int > VI; 104 typedef vector< double > VD; 105 typedef vector< VI > VVI; 106 typedef vector< SI > VSI; 107 typedef vector< PII > VPII; 108 typedef map< int, int > MII; 109 typedef map< int, string > MIS; 110 typedef map< int, PII > MIPII; 111 typedef map< PII, int > MPIII; 112 typedef map< string, int > MSI; 113 typedef map< string, string > MSS; 114 typedef map< PII, string > MPIIS; 115 typedef map< PII, PII > MPIIPII; 116 typedef multimap< int, int > MMII; 117 typedef multimap< string, int > MMSI; 118 //typedef unordered_map< int, int > uMII; 119 typedef pair< LL, LL > PLL; 120 typedef vector< LL > VL; 121 typedef vector< VL > VVL; 122 typedef priority_queue< int > PQIMax; 123 typedef priority_queue< int, VI, greater< int > > PQIMin; 124 const double EPS = 1e-8; 125 const LL inf = 0x7fffffff; 126 const LL infLL = 0x7fffffffffffffffLL; 127 const LL mod = 1e9 + 7; 128 const int maxN = 1e5 + 7; 129 const LL ONE = 1; 130 const LL evenBits = 0xaaaaaaaaaaaaaaaa; 131 const LL oddBits = 0x5555555555555555; 132 133 int N, K, ans = 0; 134 string S; 135 136 int main(){ 137 //freopen("MyOutput.txt","w",stdout); 138 //freopen("input.txt","r",stdin); 139 //INIT(); 140 scanf("%d%d", &N, &K); 141 cin >> S; 142 143 For(i, 1, S.size() - 1) if(S[i] == S[i - 1]) ++ans; 144 ans = min(ans + 2 * K, N - 1); 145 printf("%d", ans); 146 return 0; 147 }