Initial commit

Author: phoenixx1

LeetCode/200-NumberPOfIslands.cpp

@@ -0,0 +1,47 @@
+    class Solution {
+    public:
+        bool isSafe(int n, int m, int i, int j){
+            if(i<0 || i>=n){
+                return false;
+            }
+            if(j<0 || j>=m){
+                return false;
+            }
+                return true;
+        }
+
+        int numIslands(vector<vector<char>>& grid) {
+            if(grid.empty() || grid[0].empty()){
+                return 0;
+            }
+            int H = grid.size();
+            int W = grid[0].size();
+            int answer = 0;
+
+            vector<pair<int, int>> directions{{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
+
+            for(int row = 0; row < H; row++){
+                for(int col = 0; col < W; col++){
+                    if(grid[row][col] == '1'){
+                        answer++;
+                        grid[row][col] = 0;
+                        queue<pair<int, int>> q;
+                        q.push({row, col});
+                        while(!q.empty()){
+                            pair<int, int> p = q.front();
+                            q.pop();
+                            for(pair<int, int> dir : directions){
+                                int new_row = p.first + dir.first;
+                                int new_col = p.second + dir.second;
+                                if(isSafe(H, W, new_row, new_col) && grid[new_row][new_col] == '1'){
+                                    q.push({new_row, new_col});
+                                    grid[new_row][new_col] = 0;
+                                }
+                            }                        
+                        }
+                    }
+                }
+            }
+            return answer;
+        }
+    };

LeetCode/678-ValidParenthesisString.cpp

@@ -0,0 +1,23 @@
+class Solution {
+public:
+    bool checkValidString(string s) {
+        int balance = 0, stars = 0;
+        int n = s.size();
+        for(int i=0; i<n; i++){
+            if(s[i] == '(' || s[i] == '*'){
+                balance++;
+            }else if(--balance == -1){
+                return false;
+            }
+        }
+        balance = 0;
+        for(int i=n-1; i>=0; i--){
+            if(s[i] == ')' || s[i] == '*'){
+                balance++;
+            }else if(--balance == -1){
+                return false;
+            }
+        }
+        return true;
+    }
+};

SPOJ/ONP - Transform the Expression.cpp

@@ -0,0 +1,68 @@
+//author @Nishant
+
+#include <bits/stdc++.h>
+using namespace std;
+
+int prec(char opr){
+    if (opr == '+' || opr == '-')
+        return 1;
+    else if (opr == '*' || opr == '/')
+        return 2;
+    else if (opr == '^')
+        return 3;
+    else
+        return -1;
+}
+
+string infixToPostfix(const std::string &exp){
+    string postfix;
+    stack<char> stk;
+
+    for (int i = 0; exp[i]; i++){
+        if (exp[i] >= 'a' && exp[i] <= 'z' || exp[i] >= 'A' && exp[i] <= 'Z'){
+            postfix.push_back(exp[i]);
+        }else if (exp[i] == '('){
+            stk.push('(');
+        }else if (exp[i] == ')'){
+            while (!stk.empty() && stk.top() != '('){
+                postfix.push_back(stk.top());
+                stk.pop();
+            }
+            if (!stk.empty())
+                stk.pop();
+            else{
+                cerr << "Invalid infix expression: " << exp << endl;
+                exit(1);
+            }
+        }else{
+            while (!exp.empty() && prec(exp[i]) <= prec(stk.top())){
+                postfix.push_back(stk.top());
+                stk.pop();
+            }
+            stk.push(exp[i]);
+        }
+    }
+
+    while (!stk.empty()){
+        postfix.push_back(stk.top());
+        stk.pop();
+    }
+
+    return postfix;
+}
+
+int main()
+{
+
+    int i;
+    string s;
+    cin >> i;
+
+    while (i--)
+    {
+        cin >> s;
+        cout << infixToPostfix(s) << endl;
+    }
+
+    return 0;
+}