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Commit 2bd811a

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1 parent cfa7d2c commit 2bd811a

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2 files changed

+73
-19
lines changed
  • codes/java/leetcodes/src/main/java/com/hit/basmath/learn

2 files changed

+73
-19
lines changed

‎codes/java/leetcodes/src/main/java/com/hit/basmath/learn/hash_table/_1.java‎

Lines changed: 52 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -19,17 +19,61 @@
1919
* return [0, 1].
2020
*/
2121
public class _1 {
22+
/**
23+
* Solution 1: Violence method
24+
*
25+
* @param nums
26+
* @param target
27+
* @return
28+
*/
2229
public int[] twoSum(int[] nums, int target) {
23-
Map<Integer, Integer> map = new HashMap();
2430
for (int i = 0; i < nums.length; i++) {
25-
int a = nums[i];
26-
// note that the numbers in the array can be negative as well
27-
if (map.get(target - a) != null) {
28-
returnnewint[]{map.get(target - a), i};
31+
for (int j = i + 1; j < nums.length; j++) {
32+
if (nums[i] + nums[j] == target) {
33+
returnnewint[]{i, j};
34+
}
2935
}
30-
// The following should be after the check above,
31-
// otherwise it will fail for the case where target = 6 and there's a 3 in the original array.
32-
map.put(a, i);
36+
}
37+
return null;
38+
}
39+
40+
/**
41+
* Solution 2: Two pass hash table
42+
*
43+
* @param nums
44+
* @param target
45+
* @return
46+
*/
47+
public int[] twoSum2(int[] nums, int target) {
48+
Map<Integer, Integer> aMap = new HashMap<>();
49+
for (int i = 0; i < nums.length; i++) {
50+
aMap.put(nums[i], i);
51+
}
52+
for (int i = 0; i < nums.length; i++) {
53+
int complement = target - nums[i];
54+
if (aMap.containsKey(complement) &&
55+
aMap.get(complement) != i) {
56+
return new int[]{i, aMap.get(complement)};
57+
}
58+
}
59+
return null;
60+
}
61+
62+
/**
63+
* Solution 3: One pass hash table
64+
*
65+
* @param nums
66+
* @param target
67+
* @return
68+
*/
69+
public int[] twoSum3(int[] nums, int target) {
70+
Map<Integer, Integer> aMap = new HashMap<>();
71+
for (int i = 0; i < nums.length; i++) {
72+
int complement = target - nums[i];
73+
if (aMap.containsKey(complement)) {
74+
return new int[]{aMap.get(complement), i};
75+
}
76+
aMap.put(nums[i], i);
3377
}
3478
return null;
3579
}

‎codes/java/leetcodes/src/main/java/com/hit/basmath/learn/linked_list/_2.java‎

Lines changed: 21 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -18,20 +18,30 @@
1818
*/
1919
public class _2 {
2020
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
21-
ListNode prev = new ListNode(0);
22-
ListNode head = prev;
21+
ListNode dummyHead = new ListNode(0);
22+
ListNode p = l1, q = l2, curr = dummyHead;
2323
int carry = 0;
24-
while (l1 != null || l2 != null || carry != 0) {
25-
ListNode cur = new ListNode(0);
26-
int sum = ((l2 == null) ? 0 : l2.val) + ((l1 == null) ? 0 : l1.val) + carry;
27-
cur.val = sum % 10;
24+
while (p != null || q != null) {
25+
int x = (p != null) ? p.val : 0;
26+
int y = (q != null) ? q.val : 0;
27+
int sum = carry + x + y;
28+
2829
carry = sum / 10;
29-
prev.next = cur;
30-
prev = cur;
30+
curr.next = new ListNode(sum % 10);
31+
curr = curr.next;
32+
33+
if (p != null) {
34+
p = p.next;
35+
}
36+
if (q != null) {
37+
q = q.next;
38+
}
39+
}
3140

32-
l1 = (l1 == null) ? l1 : l1.next;
33-
l2 = (l2 == null) ? l2 : l2.next;
41+
if (carry > 0) {
42+
curr.next = newListNode(carry);
3443
}
35-
return head.next;
44+
45+
return dummyHead.next;
3646
}
3747
}

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