added leetcode programs

Author: diva-21

cpp/473- Matchsticks_to_Square.cpp

@@ -0,0 +1,45 @@
+class Solution {
+    int a,b,c,d;
+    bool fun(vector<int>& matchsticks,int i){
+        if(i==matchsticks.size()){
+            if(a==0 && b==0 && c==0 && d==0) return true;
+            else return false;
+        }
+        
+        if(matchsticks[i]<=a){
+            a-=matchsticks[i];
+            if(fun(matchsticks,i+1)) return true;
+            a+=matchsticks[i];
+        }
+        
+        if(matchsticks[i]<=b){
+            b-=matchsticks[i];
+            if(fun(matchsticks,i+1)) return true;
+            b+=matchsticks[i];
+        }
+        
+        if(matchsticks[i]<=c){
+            c-=matchsticks[i];
+            if(fun(matchsticks,i+1)) return true;
+            c+=matchsticks[i];
+        }
+        
+        if(matchsticks[i]<=d){
+            d-=matchsticks[i];
+            if(fun(matchsticks,i+1)) return true;
+            d+=matchsticks[i];
+        }
+		
+        return false;
+    }
+public:
+    bool makesquare(vector<int>& matchsticks) {
+        if(matchsticks.size()<4) return false;
+		int sum = accumulate(matchsticks.begin(), matchsticks.end(),0);
+        if(sum % 4 != 0) return false;
+		int sizeSum=sum/4;
+        a=sizeSum,b=sizeSum,c=sizeSum,d=sizeSum;
+		sort(matchsticks.rbegin(), matchsticks.rend());
+		return fun(matchsticks,0);
+    }
+};

cpp/52- N-Queens_2.cpp

@@ -0,0 +1,38 @@
+class Solution {
+public:
+    int queen[9];
+    bool check(int &r,int &c,int n){
+        for(int i=0;i<r;i++){
+            // here we have to check from before rows any queen(queen[i]) is placed to attk the cur level queen;
+            int pre_row=i; // previous row
+            int pre_col=queen[i]; // previous col is stored in queen[i]
+            // checking for col collison as rows cant be && and for diagonal attk
+            if(pre_col==c or abs(r-pre_row)==abs(c-pre_col)) return false;
+        }
+        return true;
+    }
+    int bt(int level,int n){
+        // base conditon
+        
+        if(level==n) return 1;
+        // return 1 as u made a board and placing queens from 0 to n-1 so u came out of board
+        
+        int ans=0;
+        // exploring choices and computation
+        for(int col=0;col<n;col++){
+            if(check(level,col,n)){
+                // check
+                queen[level]=col;
+                // move
+                ans+=bt(level+1,n);
+                queen[level]=-1;
+            }
+        }
+        // return count of ways to place queen from this row to n-1/ last row
+        return ans;
+    }
+    int totalNQueens(int n) {
+        memset(queen,-1,sizeof(queen));
+        return bt(0,n);
+    }
+};