Practise 05-Jun-2020

Author: sureshmangs

competitive programming/leetcode/2020-June-Challenge/Day-04-Reverse String.cpp

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+Write a function that reverses a string. The input string is given as an array of characters char[].
+
+Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
+
+You may assume all the characters consist of printable ascii characters.
+
+
+
+Example 1:
+
+Input: ["h","e","l","l","o"]
+Output: ["o","l","l","e","h"]
+Example 2:
+
+Input: ["H","a","n","n","a","h"]
+Output: ["h","a","n","n","a","H"]
+   Hide Hint #1
+The entire logic for reversing a string is based on using the opposite directional two-pointer approach!
+
+
+
+
+class Solution {
+public:
+    void reverseString(vector<char>& s) {
+        int n=s.size();
+        for(int i=0,j=n-1;i<n/2;i++,j--){
+            char tmp=s[i];
+            s[i]=s[j];
+            s[j]=tmp;
+        }
+    }
+
+};

competitive programming/leetcode/226. Invert Binary Tree.cpp

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+Share
+Invert a binary tree.
+
+Example:
+
+Input:
+
+     4
+   /   \
+  2     7
+ / \   / \
+1   3 6   9
+Output:
+
+     4
+   /   \
+  7     2
+ / \   / \
+9   6 3   1
+Trivia:
+This problem was inspired by this original tweet by Max Howell:
+
+Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.
+
+
+
+
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    TreeNode* invertTree(TreeNode* root) {
+        if(!root) return root;
+        queue<TreeNode*>q;
+        q.push(root);
+        while(!q.empty()){
+            TreeNode* cur = q.front();
+            q.pop();
+            swap(cur->left, cur->right);
+            if(cur->left) q.push(cur->left);
+            if(cur->right) q.push(cur->right);
+        }
+        return root;
+    }
+};

competitive programming/leetcode/344. Reverse String.cpp

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+Write a function that reverses a string. The input string is given as an array of characters char[].
+
+Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
+
+You may assume all the characters consist of printable ascii characters.
+
+
+
+Example 1:
+
+Input: ["h","e","l","l","o"]
+Output: ["o","l","l","e","h"]
+Example 2:
+
+Input: ["H","a","n","n","a","h"]
+Output: ["h","a","n","n","a","H"]
+
+
+
+
+
+class Solution {
+public:
+    void reverseString(vector<char>& s) {
+        int n=s.size();
+        for(int i=0,j=n-1;i<n/2;i++,j--){
+            char tmp=s[i];
+            s[i]=s[j];
+            s[j]=tmp;
+        }
+    }
+
+};

stack/min_stack_O(1).cpp

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+#include<iostream>
+#include<stack>
+using namespace std;
+void push(int a);
+bool isFull(int n);
+bool isEmpty();
+int pop();
+int getMin();
+
+
+stack<int> s;
+int main(){
+	int t;
+	cin>>t;
+	while(t--){
+		int n,a;
+		cin>>n;
+		while(!isEmpty()){
+		    pop();
+		}
+		while(!isFull(n)){
+			cin>>a;
+			push(a);
+		}
+		cout<<getMin()<<endl;
+	}
+}
+
+int minx;
+
+void push(int x)
+{
+     if(s.empty()){
+       s.push(x);
+       minx=x;
+   } else{
+       if(x>=minx) s.push(x);
+       else {
+           s.push(2*x-minx);
+           minx=x;
+       }
+   }
+}
+
+bool isFull(int n)
+{
+    if(s.size()==n) return true;
+    else return false;
+}
+
+bool isEmpty()
+{
+    return s.empty();
+}
+
+int pop()
+{
+    if(s.empty()) return -1;
+   if(s.top() >= minx){ int tmp=s.top();   s.pop(); return tmp; }
+   else {
+       int tmp=minx;
+       minx=2*minx-s.top();
+       s.pop();
+       return tmp;
+   }
+}
+
+int getMin()
+{
+    if(s.empty()) return -1;
+   else return minx;
+}
+
+
+int getTop(){
+    if(s.empty()) return -1;
+    if(s.top()>= minx) return s.top();
+    else return minx;
+}

stack/min_stack_extra_space.cpp

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+#include<iostream>
+#include<stack>
+using namespace std;
+void push(int a);
+bool isFull(int n);
+bool isEmpty();
+int pop();
+int getMin();
+
+
+stack<int> s;
+int main(){
+	int t;
+	cin>>t;
+	while(t--){
+		int n,a;
+		cin>>n;
+		while(!isEmpty()){
+		    pop();
+		}
+		while(!isFull(n)){
+			cin>>a;
+			push(a);
+		}
+		cout<<getMin()<<endl;
+	}
+}
+
+stack<int>ss;
+
+void push(int a)
+{
+     s.push(a);
+     if(ss.empty() || ss.top() >= a) ss.push(a);
+}
+
+bool isFull(int n)
+{
+     if(s.size()==n) return true;
+     else return false;
+}
+
+bool isEmpty()
+{
+    return s.empty();
+}
+
+int pop()
+{   if(s.empty()) return -1;
+    if(s.top()==ss.top()) ss.pop();
+    s.pop();
+}
+
+int getMin()
+{
+   if(!s.empty()) return ss.top();
+   else return -1;
+}