Create 3704.Count-No-Zero-Pairs-That-Sum-to-N.cpp

Author: wisdompeak

Recursion/3704.Count-No-Zero-Pairs-That-Sum-to-N/3704.Count-No-Zero-Pairs-That-Sum-to-N.cpp

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+using LL = long long;
+class Solution {
+    LL memo[18][2][2][2];
+    int L;
+    vector<int>digits;
+public:    
+    LL dfs(int pos, int carry, int endA, int endB) {
+        if (pos==L) {
+            if (carry==0 && endA==1 && endB==1)
+                return 1;
+            else
+                return 0;
+        }
+
+        if (memo[pos][carry][endA][endB]!=-1)
+            return memo[pos][carry][endA][endB];
+
+        LL ret = 0;
+        int target = digits[pos];
+        for (int i=0; i<=9; i++) {
+            if(endA==1 && i!=0) continue;            
+            if(endA==0 && i==0) continue;            
+            vector<int>A;
+            if (endA) A.push_back(1);
+            else {
+                A.push_back(0);
+                if (i!=0) A.push_back(1);
+            }
+
+            
+            for (int j=0; j<=9; j++) {
+                if (endB==1 && j!=0) continue;
+                if (endB==0 && j==0) continue;
+                int sum = i+j+carry;
+                if (sum%10!=target) continue;
+                int ncarry = (sum>=10)?1:0;
+
+                vector<int>B;
+                if (endB) B.push_back(1);
+                else {
+                    B.push_back(0);
+                    if (j!=0) B.push_back(1);
+                }
+
+                for (int nxt_enda: A)
+                    for (int nxt_endb: B)                                                    
+                        ret += dfs(pos+1, ncarry, nxt_enda, nxt_endb);                                                                    
+            }
+        }
+
+        memo[pos][carry][endA][endB] = ret;
+        return ret;
+           
+    };
+    
+    long long countNoZeroPairs(long long n) {
+
+        fill(&memo[0][0][0][0], &memo[0][0][0][0]+18*2*2*2, -1);
+                
+        LL temp = n;
+        while (temp>0) {
+            digits.push_back(temp%10);
+            temp/=10;
+        }
+        L = digits.size();
+        
+        return dfs(0,0,0,0);
+    }
+};