牛客 实现二叉树先序，中序和后序遍历

题目链接：https://www.nowcoder.com/practice/566f7f9d68c24691aa5abd8abefa798c?tpId=101&tqId=33229&tPage=1&rp=1&ru=/ta/programmer-code-interview-guide&qru=/ta/programmer-code-interview-guide/question-ranking

题目大意

　　略。

分析

　　用栈。

代码如下

  1 #include 
  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 < (int)(n); ++i)
  6 #define For(i,s,t) for (int i = (int)(s); i <= (int)(t); ++i)
  7 #define rFor(i,t,s) for (int i = (int)(t); i >= (int)(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()); // 删去 x 中所有 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,0x3f,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
 35 istream &operator>>(istream &in, pair &p) {
 36     in >> p.first >> p.second;
 37     return in;
 38 }
 39  
 40 template
 41 istream &operator>>(istream &in, vector &v) {
 42     for (auto &x: v)
 43         in >> x;
 44     return in;
 45 }
 46 
 47 template
 48 ostream &operator<<(ostream &out, vector &v) {
 49     Rep(i, v.size()) out << v[i] << " \n"[i == v.size() - 1];
 50     return out;
 51 }
 52  
 53 template
 54 ostream &operator<<(ostream &out, const std::pair &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
 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 vector< int > VI;
 97 typedef vector< bool > VB;
 98 typedef vector< char > VC;
 99 typedef vector< double > VD;
100 typedef vector< string > VS;
101 typedef vector< LL > VL;
102 typedef vector< VI > VVI;
103 typedef vector< VB > VVB;
104 typedef vector< VS > VVS;
105 typedef vector< VL > VVL;
106 typedef vector< VVI > VVVI;
107 typedef vector< VVL > VVVL;
108 typedef pair< int, int > PII;
109 typedef pair< LL, LL > PLL;
110 typedef pair< int, string > PIS;
111 typedef pair< string, int > PSI;
112 typedef pair< string, string > PSS;
113 typedef pair< double, double > PDD;
114 typedef vector< PII > VPII;
115 typedef vector< PLL > VPLL;
116 typedef vector< VPII > VVPII;
117 typedef vector< VPLL > VVPLL;
118 typedef vector< VS > VVS;
119 typedef map< int, int > MII;
120 typedef unordered_map< int, int > uMII;
121 typedef map< LL, LL > MLL;
122 typedef map< string, int > MSI;
123 typedef map< int, string > MIS;
124 typedef set< int > SI;
125 typedef stack< int > SKI;
126 typedef deque< int > DQI;
127 typedef queue< int > QI;
128 typedef priority_queue< int > PQIMax;
129 typedef priority_queue< int, VI, greater< int > > PQIMin;
130 const double EPS = 1e-8;
131 const LL inf = 0x7fffffff;
132 const LL infLL = 0x7fffffffffffffffLL;
133 const LL mod = 1e9 + 7;
134 const int maxN = 1e6 + 7;
135 const LL ONE = 1;
136 const LL evenBits = 0xaaaaaaaaaaaaaaaa;
137 const LL oddBits = 0x5555555555555555;
138 
139 struct TreeNode {
140     int lch = 0, rch = 0;
141 };
142 
143 int N, root;
144 TreeNode tree[maxN];
145 
146 void preOrder() {
147     SKI sk;
148     VI ret;
149     
150     sk.push(root);
151     
152     while(!sk.empty()) {
153         int rt = sk.top(); sk.pop();
154         ret.PB(rt);
155         
156         if(tree[rt].rch) sk.push(tree[rt].rch);
157         if(tree[rt].lch) sk.push(tree[rt].lch);
158     }
159     
160     Rep(i, ret.size()) printf("%d%c", ret[i], " \n"[i == ret.size() - 1]);
161 }
162 
163 void inOrder() {
164     SKI sk;
165     VI ret;
166     
167     sk.push(root);
168     
169     while(!sk.empty()) {
170         int rt = sk.top();
171         
172         if(tree[rt].lch > 0) {
173             sk.push(tree[rt].lch);
174             tree[rt].lch = -tree[rt].lch;
175         } 
176         else {
177             // 第二次回到这个节点 
178             if(tree[rt].lch < 0) tree[rt].lch = -tree[rt].lch;
179             
180             sk.pop();
181             ret.PB(rt);
182             if(tree[rt].rch) sk.push(tree[rt].rch);
183         }
184     }
185     
186     Rep(i, ret.size()) printf("%d%c", ret[i], " \n"[i == ret.size() - 1]);
187 }
188 
189 void postOrder() { // 先序遍历反过来然后做些小变动 
190     SKI sk;
191     VI ret;
192     
193     sk.push(root);
194     
195     while(!sk.empty()) {
196         int rt = sk.top(); sk.pop();
197         ret.PB(rt);
198         
199         if(tree[rt].lch) sk.push(tree[rt].lch);
200         if(tree[rt].rch) sk.push(tree[rt].rch);
201     }
202     
203     rFor(i, ret.size() - 1, 0) printf("%d%c", ret[i], " \n"[i == 0]);
204 }
205 
206 int main(){
207     //freopen("MyOutput.txt","w",stdout);
208     //freopen("input.txt","r",stdin);
209     //INIT();
210     scanf("%d%d", &N, &root);
211     Rep(i, N) {
212         int fa, lch, rch;
213         scanf("%d%d%d", &fa, &lch, &rch);
214         
215         tree[fa].lch = lch;
216         tree[fa].rch = rch;
217     }
218     
219     preOrder();
220     inOrder();
221     postOrder();
222     return 0;
223 }

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转载于:https://www.cnblogs.com/zaq19970105/p/11352116.html