refer: product-of-array-except-self

Author: mkwkw

validate-binary-search-tree/mkwkw.cpp

@@ -1 +1,81 @@
-//set-up
+//Optimize complexity
+class Solution {
+public:
+    vector<int> productExceptSelf(vector<int>& nums) {
+        
+        vector<int> answer(nums.size(), 1);
+        //production before nums[i] from index 0
+        int before = 1;
+
+        for(int i=0; i<nums.size()-1; i++)
+        {
+            before *= nums[i];
+            answer[i+1] *= before;
+        }
+
+        //nums[i] 기준 앞에서 production 해놓은 것에 nums[i] 기준 뒤에 것들을 production from index n-1
+        //production after nums[i] to answer[i-1]
+        // answer[i-1] * after
+        int after = 1;
+        for(int i=nums.size()-1; i>0; i--)
+        {
+            after *= nums[i];
+            answer[i-1] *= after;
+        }
+
+        return answer;
+    }
+};
+
+
+
+//using division operation
+/*
+class Solution {
+public:
+    vector<int> productExceptSelf(vector<int>& nums) {
+        int zeroCnt = 0;
+        int allProduct = 1;
+        vector<int> answer(nums.size());
+
+        for(int i=0; i<nums.size(); i++)
+        {
+            allProduct *= nums[i];
+            if(nums[i]==0)
+            {
+                zeroCnt++;
+            }
+        }
+
+        if(zeroCnt == 0)
+        {
+            for(int i=0; i<nums.size(); i++)
+            {
+                answer[i] = allProduct/nums[i];
+            }
+        }
+        else if(zeroCnt == 1)
+        {
+            int zeroIdx = 0;
+            int allProductWithoutZero = 1;
+
+            for(int i=0; i<nums.size(); i++)
+            {
+                if(nums[i]==0)
+                {
+                    zeroIdx = i;
+                }
+                else
+                {
+                    allProductWithoutZero *=nums[i];
+                    answer[i] = 0;
+                 }
+            }
+
+            answer[zeroIdx] = allProductWithoutZero;
+        }
+        
+        return answer;
+    }
+};
+*/