added leetcode programs

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);
+ }
+};