Add day22

Jongeun/Day22/51. N_Queens.cpp

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+class Solution
+{
+public:
+    vector<vector<string>> solveNQueens(int n)
+    {
+        vector<vector<string>> result;
+        vector<string> board;
+        for (int i = 0; i < n; i++)
+        {
+            string temp = "";
+            for (int j = 0; j < n; j++)
+            {
+                temp.push_back('.');
+            }
+            board.push_back(temp);
+        }
+        vector<int> col(n + 1);
+        _solveNQueens(result, col, board, 0, n);
+
+        return result;
+    }
+
+    void _solveNQueens(vector<vector<string>> &result, vector<int> &col, vector<string> &board, int step, int n)
+    {
+        if (isPromising(col, step))
+        {
+            if (step == n)
+            {
+                // push the col
+                for (int i = 1; i < n + 1; i++)
+                {
+                    board[i - 1][col[i] - 1] = 'Q';
+                }
+                result.push_back(board);
+
+                // restore
+                for (int i = 1; i < n + 1; i++)
+                {
+                    board[i - 1][col[i] - 1] = '.';
+                }
+
+                return;
+            }
+            else
+            {
+                for (int j = 1; j < n + 1; j++)
+                {
+                    col[step + 1] = j;
+                    _solveNQueens(result, col, board, step + 1, n);
+                }
+            }
+        }
+    }
+
+    bool isPromising(vector<int> &col, int step)
+    {
+        if (step == 0)
+        {
+            return true;
+        }
+
+        int j = 1;
+        while (j < step)
+        {
+            if (col[step] == col[j] || abs(col[step] - col[j]) == (step - j))
+            {
+                return false;
+            }
+            j++;
+        }
+
+        return true;
+    }
+};

Jongeun/Day22/70_ClimbingStairs.cpp

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+class Solution
+{
+public:
+    int climbStairs(int n)
+    {
+        vector<int> table(46);
+        table[0] = 1;
+        table[1] = 1;
+        for (int i = 2; i < n + 1; i++)
+        {
+            table[i] = table[i - 1] + table[i - 2];
+        }
+
+        return table[n];
+    }
+};

Jongeun/Day22/746_MinCostClimbingStairs.cpp

@@ -0,0 +1,17 @@
+class Solution
+{
+public:
+    int minCostClimbingStairs(vector<int> &cost)
+    {
+        int size = cost.size();
+        int first = 0;
+        int second = 0;
+        for (int i = 0; i < size - 1; i++)
+        {
+            int tempt = second;
+            second = min(first + cost[i], second + cost[i + 1]);
+            first = tempt;
+        }
+        return second;
+    }
+};