Edit distance(dynamic programing)
题目描述
Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.)You have the following 3 operations permitted on a word:a) Insert a character
b) Delete a character
c) Replace a character
题目解析
代码实现
int min3(int a, int b, int c)
{
return (a < b) ? (a < c ? a : c) : (b < c ? b : c);
}
int minDistance(string word1, string word2) {
//准备工作:获取字符串长度
int strlen1 = word1.size();
int strlen2 = word2.size();
//准备工作:新建dp矩阵
vector<vector<int> >dp(strlen1 + 1, vector<int>(strlen2 + 1, 0));
//第一步:第一行,第一列分别置i
for (int i = 1; i <= strlen1; i++)
dp[i][0] = i;
for (int i = 1; i <= strlen2; i++)
dp[0][i] = i;
//第二步:双层for循环进行递推
for (int i = 1; i <= strlen1; i++)
{
for (int j = 1; j <= strlen2; j++)
{
int diff;
if (word1[i - 1] == word2[j - 1])
diff = 0;
else
diff = 1;
dp[i][j] = min3(dp[i - 1][j] + 1, dp[i][j - 1] + 1, dp[i - 1][j - 1] + diff);
}
}
return dp[strlen1][strlen2];
}
Add two numbers
题目描述
You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
题目分析
链表版的两个数相加的题,题目是从个位到十位到百位……因此还是比较简单。
代码实现
ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
if (l1 == NULL)
return l2;
if (l2 == NULL)
return l1;
ListNode *result=new ListNode(-1);
ListNode *p1 = l1;
ListNode *p2 = l2;
ListNode *p = result;
int v = 0;
int jin = 0;
while (p1 != NULL || p2 != NULL||jin)
{
v = (p1 ? p1->val : 0) + (p2 ? p2->val : 0) + jin;
jin = v / 10;
v %= 10;
ListNode *newnode = new ListNode(v);
p->next = newnode;
p = p->next;
if (p1)
p1 = p1->next;
if (p2)
p2 = p2->next;
}
return result->next;
}
partition list
题目描述
Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.You should preserve the original relative order of the nodes in each of the two partitions.For example,
Given1->4->3->2->5->2and x = 3,
return1->2->2->4->3->5.
题目解析
最简单的方法,新建两个链表l1和l2,l1存放小于指定数字的链表部分,l2存放大于等于指定数字的链表部分。然后把他们拼接起来。
代码实现
ListNode *partition(ListNode *head, int x)
{
ListNode *plist1 = new ListNode(0);
ListNode *plist2 = new ListNode(0);
ListNode *list1 = plist1;
ListNode *list2 = plist2;
while (head != NULL)
{
if (head->val < x)
{
ListNode *newnode = new ListNode(0);
newnode->val = head->val;
newnode->next = NULL;
list1->next = newnode;
list1 = list1->next;
}
else if (head->val >= x)
{
ListNode *bignode = new ListNode(0);
bignode->val = head->val;
bignode->next = NULL;
list2->next = bignode;
list2 = list2->next;
}
head = head->next;
}
list1->next = plist2->next;
plist2->next = NULL;
return plist1->next;
}
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