内置容器的排序规则构造方式
转自：http://lhearen.top/2016/08/27/Sort-for-Built-in-Containers/
C ++中有很多内置的容器，我们可以轻松有效地实现我们想要的内容。 然而，有时它们的排序能力相对有限，因此，我们必须提出自定义比较器来重新定义排序功能。
几乎所有的函数/容器（例如priority_queue除外）都要求排序满足严格弱排序的标准数学定义，否则函数/容器的行为将不会被定义。
- 方法：
-
定义 operator<()
如果你希望自定义类的对象能够像往常的原始类型一样自然排序，则可以使用此方法。 如果要保持原有的排序特性，返回<，否则>。（此处用>表示 重载了运算符<号）
1 class Edge{ 2 public: 3 int from, to , weight; 4 Edge(int a, int b, int c): from(a), to(b), weight(c){} 5 bool operator < (Edge other) const{ 6 return weight < other.weight; 7 } 8 }; 9 int main() 10 { 11 vector<Edge> edges; 12 for(int i = 0; i < 10; ++i) edges.emplace_back(i, i+2, 20-i); 13 cout<<"Original vector: "<<endl; 14 for(int i = 0; i < 10; ++i) cout<<edges[i].weight<<","; 15 cout<<endl; 16 cout<<"Sorted ascending vector: "<<endl; 17 sort(edges.begin(), edges.end()); 18 for(int i = 0; i < 10; ++i) cout<<edges[i].weight<<","; 19 cout<<endl; 20 random_shuffle(edges.begin(), edges.end()); 21 cout<<"Shuffled vector: "<<endl; 22 for(int i = 0; i < 10; ++i) cout<<edges[i].weight<<","; 23 cout<<endl; 24 cout<<"Ascending set: "<<endl; 25 set<Edge> edgeSet(edges.begin(), edges.end()); 26 for(auto e: edgeSet) cout<<e.weight<<","; 27 cout<<endl; 28 cout<<"Keys ascending map: "<<endl; 29 map<Edge, int> edgeMap; 30 for(int i = 0; i < edges.size(); ++i) edgeMap[edges[i]] = i*5; 31 for(auto& pair: edgeMap) cout<<"key: "<<pair.first.weight<<","; 32 cout<<endl; 33 cout<<"Descending max heap: "<<endl; 34 priority_queue<Edge> maxHeap(edges.begin(), edges.end()); 35 while(maxHeap.size()){ 36 cout<<maxHeap.top().weight<<","; 37 maxHeap.pop(); 38 } 39 cout<<endl; 40 return 0; 41 }
输出如下：
1 Original vector: 2 20,19,18,17,16,15,14,13,12,11, 3 Sorted ascending vector: 4 11,12,13,14,15,16,17,18,19,20, 5 Shuffled vector: 6 17,11,14,16,18,19,15,12,13,20, 7 Ascending set: 8 11,12,13,14,15,16,17,18,19,20, 9 Keys ascending map: 10 key: 11,key: 12,key: 13,key: 14,key: 15,key: 16,key: 17,key: 18,key: 19,key: 20, 11 Descending max heap: 12 20,19,18,17,16,15,14,13,12,11,
Set and map
1 struct cmpClass{ 2 bool operator()(const int& a, const int& b) const { 3 return a > b; 4 } 5 }; 6 int main() 7 { 8 int myints[] = {10, 60, 50, 20}; 9 vector<int> v(myints, myints+4); 10 auto cmpFunc = [](const int a, const int b) { return a > b; }; 11 cout<<"Sorted int vector using lambda function: "<<endl; 12 sort(v.begin(), v.end(), [](const int a, const int b) { return a < b; }); 13 for(int i = 0; i < v.size(); ++i) cout<<v[i]<<","; 14 cout<<endl; 15 random_shuffle(v.begin(), v.end()); 16 cout<<"Shuffled int vector: "<<endl; 17 for(int i = 0; i < v.size(); ++i) cout<<v[i]<<","; 18 cout<<endl; 19 sort(v.begin(), v.end(), cmpFunc); 20 cout<<"Sorted int vector using cmpFunc: "<<endl; 21 for(int i = 0; i < v.size(); ++i) cout<<v[i]<<","; 22 cout<<endl; 23 cout<<"Ascending int set using less<int>: "<<endl; 24 set<int, less<int>> lessSet(v.begin(), v.end()); 25 for(auto n: lessSet) cout<<n<<","; 26 cout<<endl; 27 cout<<"Descending int set using cmpFunc: "<<endl; 28 set<int, decltype(cmpFunc)> funcSet(cmpFunc); 29 for(int i = 0; i < v.size(); ++i) funcSet.insert(v[i]); 30 for(auto n: funcSet) cout<<n<<","; 31 cout<<endl; 32 cout<<"Descending int set using cmpClass: "<<endl; 33 set<int, cmpClass> classSet(v.begin(), v.end()); 34 for(auto n: classSet) cout<<n<<","; 35 cout<<endl; 36 cout<<"Descending keys in map using greater<int>: "<<endl; 37 map<int, int, greater<int>> greaterMap; 38 for(int i = 0; i < v.size(); ++i) greaterMap[v[i]] = v[i]*3; 39 for(auto& pair: greaterMap) cout<<"key: "<<pair.first<<","; 40 cout<<endl; 41 cout<<"Descending keys in map using cmpFunc: "<<endl; 42 map<int, int, decltype(cmpFunc)> funcMap(cmpFunc); 43 for(int i = 0; i < v.size(); ++i) funcMap[v[i]] = 2*v[i]; 44 for(auto& pair: funcMap) cout<<"key: "<<pair.first<<","; 45 cout<<endl; 46 cout<<"Descending keys in map using cmpClass: "<<endl; 47 map<int, int, cmpClass> classMap; 48 for(int i = 0; i < v.size(); ++i) classMap[v[i]] = 3*v[i]; 49 for(auto& pair: classMap) cout<<"key: "<<pair.first<<","; 50 cout<<endl; 51 return 0; 52 }
输出如下：
1 Sorted int vector using lambda function: 2 10,20,50,60, 3 Shuffled int vector: 4 10,60,50,20, 5 Sorted int vector using cmpFunc: 6 60,50,20,10, 7 Ascending int set using less<int>: 8 10,20,50,60, 9 Descending int set using cmpFunc: 10 60,50,20,10, 11 Descending int set using cmpClass: 12 60,50,20,10, 13 Descending keys in map using greater<int>: 14 key: 60,key: 50,key: 20,key: 10, 15 Descending keys in map using cmpFunc: 16 key: 60,key: 50,key: 20,key: 10, 17 Descending keys in map using cmpClass: 18 key: 60,key: 50,key: 20,key: 10,
Priority_queue
- primitive types including int, float, …, and pair;
cmpClassfor comparer;cmpFunctionfor comparer.
1 struct cmpClass{ 2 bool operator()(const int a, const int b) const { 3 return a < b; 4 } 5 }; 6 int main() 7 { 8 int myints[] = {10, 60, 50, 20}; 9 vector<int> v(myints, myints+4); 10 cout<<"Sorted ascending vector using less<int>: "<<endl; 11 sort(v.begin(), v.end(), less<int>()); 12 for(int i = 0; i < v.size(); ++i) cout<<v[i]<<","; 13 cout<<endl; 14 cout<<"Min heap using greater<int>: "<<endl; 15 priority_queue<int, vector<int>, greater<int>> minIntHeap(myints, myints+4); 16 while(minIntHeap.size()) { 17 cout<<minIntHeap.top()<<","; 18 minIntHeap.pop(); 19 } 20 cout<<endl; 21 vector<pair<int, int>> vv; 22 for(int i = 0; i < 10; ++i) vv.emplace_back(20-i, i); 23 cout<<"Unsorted pair vector: "<<endl; 24 for(int i = 0; i < vv.size(); ++i) cout<<vv[i].first<<","; 25 cout<<endl; 26 cout<<"Sorted ascending pair vector: "<<endl; 27 sort(vv.begin(), vv.end(), less<pair<int, int>>()); 28 for(int i = 0; i < vv.size(); ++i) cout<<vv[i].first<<","; 29 cout<<endl; 30 cout<<"Min heap using greater<pair<int, int>>: "<<endl; 31 priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> minPairHeap(vv.begin(), vv.end()); 32 while(minPairHeap.size()){ 33 cout<<minPairHeap.top().second<<","; 34 minPairHeap.pop(); 35 } 36 cout<<endl; 37 cout<<"Max heap using cmpClass to compare int: "<<endl; 38 priority_queue<int, vector<int>, cmpClass> maxClassHeap(v.begin(), v.end()); 39 while(maxClassHeap.size()){ 40 cout<<maxClassHeap.top()<<","; 41 maxClassHeap.pop(); 42 } 43 cout<<endl; 44 cout<<"Min heap using cmpFunc to compare int: "<<endl; 45 auto cmpFunction = [](const int a, const int b) { return a > b; }; 46 priority_queue<int, vector<int>, decltype(cmpFunction)> minFuncHeap(cmpFunction); 47 for(int i = 0; i < v.size(); ++i) minFuncHeap.push(v[i]); 48 while(minFuncHeap.size()){ 49 cout<<minFuncHeap.top()<<","; 50 minFuncHeap.pop(); 51 } 52 cout<<endl; 53 return 0; 54 }
输出如下：
1 Sorted ascending vector using less<int>: 2 10,20,50,60, 3 Min heap using greater<int>: 4 10,20,50,60, 5 Unsorted pair vector: 6 20,19,18,17,16,15,14,13,12,11, 7 Sorted ascending pair vector: 8 11,12,13,14,15,16,17,18,19,20, 9 Min heap using greater<pair<int, int>>: 10 9,8,7,6,5,4,3,2,1,0, 11 Max heap using cmpClass to compare int: 12 60,50,20,10, 13 Min heap using cmpFunc to compare int: 14 10,20,50,60,
- a more complex usage for funcCmp.
1 auto cmp = [&nums1, &nums2](const pair<int, int>& a, const pair<int, int>&b) { 2 return nums1[a.first]+nums2[a.second] > nums1[b.first]+nums2[b.second]; }; 3 priority_queue<pair<int, int>, vector<pair<int, int>>, decltype(cmp)> minHeap(cmp);
Basics
- Access the inner map via the outer map
auto inner_map = cost_function.find(c0); int minCost = inner_map->second.find(c1)->second;
