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238ProductofArrayExceptSelf.java
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238ProductofArrayExceptSelf.java
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public int[] productExceptSelf(int[] nums) {
if (nums == null || nums.length == 0) return nums;
int sum = 1;
int hasZero = 0;
for (int num: nums) {
if (num != 0) sum *= num;
else hasZero++;
}
if (hasZero > 1) sum = 0;
for (int i = 0; i < nums.length; i++) {
if (nums[i] == 0) nums[i] = sum;
else {
if (hasZero > 0) nums[i] = 0;
else nums[i] = sum / nums[i];
}
}
return nums;
}
//revised version, no extra space used, O(n) time complexity
public int[] productExceptSelf(int[] nums) {
if(nums == null || nums.length == 0) return nums;
int l = nums.length;
int[] res = new int[l];
res[0] = 1;
for(int i = 1; i < l; i++) {
res[i] = res[i - 1] * nums[i - 1];
}
int former = 1;
for(int i = l - 1; i >= 0; i--) {
res[i] *= former;
former *= nums[i];
}
return res;
}
public class Solution {
public int[] productExceptSelf(int[] nums) {
if(nums == null) return nums;
int length = nums.length;
int[] preorder = new int[length];
preorder[0] = 1;
int[] postorder = new int[length];
postorder[0] = 1;
int[] res = new int[length];
for(int i = 1; i < length; i++) {
preorder[i] = preorder[i-1] * nums[i - 1];
postorder[i] = postorder[i-1] * nums[length - i];
}
for(int i = 0; i < length; i++) {
res[i] = preorder[i] * postorder[length - 1 - i];
}
return res;
}
}