product of array except self PR

Author: haung921209

product-of-array-except-self/haung921209.md

@@ -0,0 +1,44 @@
+- URL : https://leetcode.com/problems/product-of-array-except-self/description/
+- points from constraints
+  - 2 <= nums.length <= 10^5
+    - if not use O(n) algorithm, a TLE occurs
+  - -30 <= nums[i] <= 30
+    - the production result can be negative
+    - do not use an unsigned type for the result object.
+  - The input is generated such that answer[i] is guaranteed to fit in a 32-bit integer.
+    - There is no need to use a 64-bit (or larger) type for the result object.
+    - However, it is not guaranteed that the intermediate object will always be a 32-bit type.
+
+
+
+```cpp
+class Solution {
+public:
+    vector<int> productExceptSelf(vector<int>& nums) {
+        vector<int> idxOfZero;
+        long long productRes = 1;
+        for(int i=0;i<nums.size();i++){
+            if(nums[i]==0){
+                idxOfZero.push_back(i);
+            }else{
+                productRes *=nums[i];
+            }
+        }
+        vector<int> res(nums.size(), 0);
+        if(idxOfZero.size()>=2){
+            return res;
+        }else if(idxOfZero.size()==1){
+            res[idxOfZero[0]] = productRes;
+            return res;
+        }
+
+        for(int i=0;i<nums.size();i++){
+            res[i] = (int)(productRes / nums[i]);
+        }
+        return res;
+    }
+};
+```
+
+- O(n)
+- long long type for result object -> 64bit(by constraint #3)