Create 1896.Minimum-Cost-to-Change-the-Final-Value-of-Expression.cpp

Stack/1896.Minimum-Cost-to-Change-the-Final-Value-of-Expression/1896.Minimum-Cost-to-Change-the-Final-Value-of-Expression.cpp

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+class Solution {
+public:
+    int evalVal(char op, pair<int,int>&a, pair<int,int>&b)
+    {                        
+        if (op == '#')
+            return b.first;
+        else if (op == '&')                    
+            return a.first & b.first;
+        else
+            return a.first | b.first;
+    }
+
+    // 1. 1|1，需要翻转一个数字，同时翻转运算符 
+    // 2. 0|0，需要翻转一个数字
+    // 3. 0|1，需要翻转运算符
+    // 4. 1&1，需要翻转一个数字
+    // 5. 0&0，需要翻转一个数字，同时翻转运算符 
+    // 6. 0&1，需要翻转运算符
+    int evalFlip(char op, pair<int,int>&a, pair<int,int>&b)
+    {               
+        if (op == '#')
+            return b.second;        
+        else if (op=='&')
+        {
+            if (a.first + b.first == 2)
+                return min(a.second, b.second);
+            else if (a.first + b.first == 1)
+                return 1;
+            else
+                return min(a.second, b.second)+1;
+
+        }
+        else
+        {
+            if (a.first + b.first == 2)
+                return min(a.second, b.second)+1;
+            else if (a.first + b.first == 1)
+                return 1;
+            else
+                return min(a.second, b.second);
+        }                
+    }
+
+    int minOperationsToFlip(string expression) 
+    {
+        stack<pair<int,int>>s1; // {val, # of operations to flip this value}
+        stack<char>s2;
+        pair<int,int> cur = {-1, -1};
+        char op = '#';
+
+        int ret = 0;
+        expression = "(" + expression + ")";
+
+        for (auto ch:expression)
+        {
+            if (ch=='&'||ch=='|')
+                op = ch;
+            else if (ch=='0' || ch=='1')
+            {
+                pair<int,int> nxt = {ch-'0', 1};
+                int val = evalVal(op, cur, nxt);
+                int flip = evalFlip(op, cur, nxt);                               
+                cur = {val, flip};
+                ret = flip;
+            }
+            else if (ch=='(')
+            {                
+                s1.push(cur);
+                s2.push(op);
+                cur = {-1, -1};
+                op = '#';
+            }
+            else
+            {
+                auto last = s1.top();
+                s1.pop();
+                char op = s2.top();
+                s2.pop();
+
+                int val = evalVal(op, last, cur);
+                int flip = evalFlip(op, last, cur);
+                cur = {val, flip};
+                ret = flip;
+            }
+        }
+
+        return ret; 
+    }
+};
+