#238 solution

Author: ys-han00

product-of-array-except-self/ys-han00.cpp

@@ -1,27 +1,69 @@
+// class Solution {
+// public:
+//     vector<int> productExceptSelf(vector<int>& nums) {
+//         int mul = 1, zero_cnt = 0;
+
+//         for(int i = 0; i < nums.size(); i++) {
+//             if(nums[i] != 0)
+//                 mul *= nums[i];
+//             else
+//                 zero_cnt++;
+//         }
+
+//         vector<int> ans = vector<int>(nums.size(), 0);
+                
+//         if(zero_cnt == 1) {
+//             for(int i = 0; i < nums.size(); i++) {
+//                 if(nums[i] == 0) {
+//                     ans[i] = mul;
+//                     break;
+//                 }
+//             }
+//         } else if(zero_cnt == 0) {
+//             for(int i = 0; i < nums.size(); i++)
+//                 ans[i] = mul / nums[i];
+//         }
+
+//         return ans;
+//     }
+// };
+
+// class Solution {
+// public:
+//     vector<int> productExceptSelf(vector<int>& nums) {
+//         int mul = 1, zero_cnt = 0;
+//         vector<int> prefix(nums.size(), 0), postfix(nums.size(), 0);
+
+//         prefix[0] = 1;
+//         for(int i = 1; i < nums.size(); i++)
+//             prefix[i] = nums[i - 1] * prefix[i - 1];
+
+//         postfix[nums.size() - 1] = 1;
+//         for(int i = nums.size() - 2; i >= 0; i--)
+//             postfix[i] = nums[i + 1] * postfix[i + 1];
+
+//         vector<int> ans = vector<int>(nums.size(), 0);
+//         for(int i = 0; i < nums.size(); i++)
+//             ans[i] = postfix[i] * prefix[i];
+
+//         return ans;
+//     }
+// };
+
 class Solution {
 public:
     vector<int> productExceptSelf(vector<int>& nums) {
-        int mul = 1, zero_cnt = 0;
+        vector<int> ans(nums.size(), 1);
+        int before = 1, after = 1;
 
-        for(int i = 0; i < nums.size(); i++) {
-            if(nums[i] != 0)
-                mul *= nums[i];
-            else
-                zero_cnt++;
+        for(int i = 0; i < nums.size() - 1; i++) {
+            before *= nums[i];
+            ans[i + 1] *= before;
         }
 
-        vector<int> ans = vector<int>(nums.size(), 0);
-                
-        if(zero_cnt == 1) {
-            for(int i = 0; i < nums.size(); i++) {
-                if(nums[i] == 0) {
-                    ans[i] = mul;
-                    break;
-                }
-            }
-        } else if(zero_cnt == 0) {
-            for(int i = 0; i < nums.size(); i++)
-                ans[i] = mul / nums[i];
+        for(int i = nums.size() - 1; i > 0; i--) {
+            after *= nums[i];
+            ans[i - 1] *= after;
         }
 
         return ans;