64 lines
1.3 KiB
Plaintext
64 lines
1.3 KiB
Plaintext
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// A Stack based C++ program to find next
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// greater element for all array elements
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// in same order as input.
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#include <bits/stdc++.h>
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using namespace std;
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/* prints element and NGE pair for all
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elements of arr[] of size n */
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void printNGE(int arr[], int n)
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{
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stack<int> s;
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unordered_map<int, int> mp;
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/* push the first element to stack */
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s.push(arr[0]);
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// iterate for rest of the elements
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for (int i = 1; i < n; i++) {
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if (s.empty()) {
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s.push(arr[i]);
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continue;
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}
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/* if stack is not empty, then
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pop an element from stack.
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If the popped element is smaller
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than next, then
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a) print the pair
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b) keep popping while elements are
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smaller and stack is not empty */
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while (s.empty() == false && s.top() < arr[i]) {
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mp[s.top()] = arr[i];
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s.pop();
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}
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/* push next to stack so that we can find
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next smaller for it */
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s.push(arr[i]);
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}
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/* After iterating over the loop, the remaining
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elements in stack do not have the next smaller
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element, so print -1 for them */
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while (s.empty() == false) {
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mp[s.top()] = -1;
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s.pop();
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}
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for (int i=0; i<n; i++)
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cout << arr[i] << " ---> " << mp[arr[i]] << endl;
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}
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/* Driver program to test above functions */
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int main()
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{
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int arr[] = { 11, 13, 21, 3 };
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int n = sizeof(arr) / sizeof(arr[0]);
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printNGE(arr, n);
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return 0;
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}
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