Traversing a map (or unordered_map) in C++ STL
We can traverse map and unordered_map using following different ways.
Using a range based for loop
map
// CPP program to traverse a map using range // based for loop #include <bits/stdc++.h> using namespace std; int main() { int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 }; int n = sizeof(arr) / sizeof(arr[0]); map<int, int> m; for (int i = 0; i < n; i++) m[arr[i]]++; cout << "Element Frequency" << endl; for (auto i : m) cout << i.first << " " << i.second << endl; return 0; } |
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unordered_map
// CPP program to traverse a unordered_map using // range based for loop #include <bits/stdc++.h> using namespace std; int main() { int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 }; int n = sizeof(arr) / sizeof(arr[0]); unordered_map<int, int> m; for (int i = 0; i < n; i++) m[arr[i]]++; cout << "Element Frequency" << endl; for (auto i : m) cout << i.first << " " << i.second << endl; return 0; } |
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Output [NOTE: For unordered_map output rows can be
in any order]
Element Frequency 1 4 2 1 3 2 4 1
Traversing using begin() and end()
map
// CPP program to traverse a map using iterators #include <bits/stdc++.h> using namespace std; int main() { int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 }; int n = sizeof(arr) / sizeof(arr[0]); map<int, int> m; for (int i = 0; i < n; i++) m[arr[i]]++; cout << " Element Frequency" << endl; for (auto i = m.begin(); i != m.end(); i++) cout << i->first << " " << i->second << endl; return 0; } |
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unordered_map
// CPP program to traverse a unordered_map // using iterators #include <bits/stdc++.h> using namespace std; int main() { int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 }; int n = sizeof(arr) / sizeof(arr[0]); unordered_map<int, int> m; for (int i = 0; i < n; i++) m[arr[i]]++; cout << " Element Frequency" << endl; for (auto i = m.begin(); i != m.end(); i++) cout << i->first << " " << i->second << endl; return 0; } |
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Output [NOTE: For unordered_map output rows can be
in any order]
Element Frequency 1 4 2 1 3 2 4 1
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