版本比较
比较
标识
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- 该行被删除。
- 格式已经改变。
通用变量命名
常用变量命名
| 变量类型 | 变量名 |
|---|---|
| 索引 | index，idx |
| 数组 | arr，array |
| 左、中、右 | left，mid，right，l，m，r |
| 和、差、商、积 | sum、diff、quot(ient)、prod(uct) |
| 边的起点、终点、权值 | u、v、w |
| 图、队列、栈等命名 | 单大写字母，比如G、Q、S。 |
二分查找
| 代码块 |
|---|
int binary_search(int a[], int n, int val) {
int ret = -1; // 查找失败返回-1
int left = 0;
int right = n - 1;
int mid;
while(left <= right) {
mid = left + (right - left) / 2; // 防止直接平均可能的溢出问题
if(a[mid] < val) {
left = mid + 1;
} else if(a[mid] > val) {
right = mid - 1;
} else { // 相等情况放到最后，减少分支预测，因为多数搜索情况不是大于就是小于
ret = mid;
break;
}
}
return ret;
} |
二维前缀和
| 代码块 |
|---|
sum[x][y] = grid[x][y] + sum[x-1][y] + sum[x][y-1] - sum[x-1][y-1]
area(x1,y1,x2,y2) = sum[x2][y2] - sum[x2][y1-1] - sum[x1-1][y2] + sum[x1-1][y1-1] |
邻接矩阵DFS & BFS
| 代码块 |
|---|
#define MAXN 1005 int G[MAXN][MAXN]; // 邻接矩阵 int n; // 顶点数 bool visited[MAXN]; // 记录顶点是否已访问 void DFS_AM(int u) { cout << u << " "; visited[u] = true; for(int i = 0; i < n; i++) { if(G[u][i] && !visited[i]) { DFS_AM(i); } } } void BFS_AM(int u) { queue<int> Q; cout << u << " "; visited[u] = true; Q.push(u); while(!Q.empty()) { int v = Q.front(); Q.pop(); for(int i = 0; i < n; i++) { // 依次检查v的所有邻接点 if(G[v][i] && !visited[i]) { // v、i相邻且i未被访问 cout << i << " "; visited[i] = true; Q.push(i); } } |
邻接矩阵DFS代码模板
}
} |
邻接表DFS & BFS
| 代码块 |
|---|
#define MAXN 1000
vector<int> G[MAXN]; // 邻接表
int n; // 顶点数
bool visited[MAXN]; // 记录顶点是否已访问
void DFS_AL(int u) {
cout << u << " ";
visited[u] = true;
for(auto &i : G[u]) {
if(!visited[i]) {
DFS_AL(i);
}
}
}
void BFS_AL(int u) {
queue<int> Q;
cout << u << " ";
visited[u] = true;
Q.push(u);
while(!Q.empty()) {
int v = Q.front();
Q.pop();
for(auto &i : G[v]) { // 依次检查v的所有邻接点
if(!visited[i]) {
cout << i << " ";
visited[i] = true;
Q.push(i);
}
}
}
} |
网格图的DFS
| 代码块 |
|---|
vector<vector<int>> grid;
vector<vector<int>> visited;
void dfs( |
| 代码块 |
vector<vector<int>> visited; void dfs(vector<vector<int>> &grid, int x, int y) { static int dx[] = {-1, 0, 1, 0}; static int dy[] = {0, 1, 0, -1}; visited[x][y] = true; // 标记已访问 for(int i = 0; i < 4; i++) { // 遍历上下左右邻接点对上下左右四个邻接点进行递归dfs int tx = x + dx[i]; int ty = y + dy[i]; if(tx < 0 || ty < 0 || tx >= grid.size() || ty >= grid[0].size() || visited[txx][tyy]) { continue; // 出界或已访问过 } else { dfs(grid, tx, ty); } } } |
链表
邻接表BFS代码模板TODO链表定义
| 代码块 |
|---|
// 单向链表
struct ListNode {
int val;
ListNode *next;
ListNode() : val(0), next(nullptr) {}
ListNode(int x) : val(x), next(nullptr) {}
ListNode(int x, ListNode *next) : val(x), next(next) {}
};
// 双向链表
struct Node {
int val;
Node *prev;
Node *next;
}; |
反转单链表
| 代码块 |
|---|
ListNode* reverseList(ListNode* head) {
if(!head || !(head->next)) {
return head;
}
ListNode *pre = head;
ListNode *p = head->next;
ListNode *next;
while(p) {
next = p->next;
p->next = pre;
pre = p;
p = next;
}
head->next = nullptr;
return pre;
} |
二叉树
结点定义
| 代码块 |
|---|
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode() : val(0), left(nullptr), right(nullptr) {}
TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
}; |
构建
| 代码块 |
|---|
// 从数组v的cur位置开始构建二叉树 // 数组v代表对应的满二叉树的层次遍历结果，节点编号从0开始，如果某个结点为空，则用'#'填充 TreeNode* createTree(vector<int> &v, int cur) { if(v[cur] == '#') return nullptr; TreeNode *root = new TreeNode(v[cur]); int left = cur * 2 + 1; // 满二叉树层次遍历，节点i的左孩子编号必为2i+1 int right = cur * 2 + 2; // 右孩子的编号为2i+2 if(left <= v.size() - 1) { root->left = createTree(v, left); } else { root->left = nullptr; } if(right <= v.size() - 1) { root->right = createTree(v, rightvector<int> visited; void bfs(vector<vector<int>> &graph, int start) { queue<int> q; q.push(start); visited[start] = 1; while(!q.empty()) { int size = q.size(); while(size-- > 0) { int cur = q.front(); q.pop(); } else { visited[cur] = 1 root->right = nullptr; } return root; } |
递归遍历
| 代码块 |
|---|
void preorder(TreeNode *root) { if(!root) return; cout << root->val << " "; for(auto next : graph[cur] preorder(root->left); preorder(root->right); } void inorder(TreeNode *root) { if(!root) return; preorder(root->left); cout << root->val << " "; preorder(root->right); } void postorder(TreeNode *root) { if(!root) return; preorder(root->left); preorder(root->right); cout << root->val << " "; } |
非递归遍历
| 代码块 |
|---|
void preorder(TreeNode *rootvisited[next]) { stack<TreeNode*> stk; TreeNode *cur = root; while(cur || !stk.empty()) q.push(next);{ while(cur) { cout << cur->val << " "; visited[next] = 1 stk.push(cur); cur = cur->left; } cur = stk.top(); }stk.pop(); }cur = cur->right; } } |
反转单链表
| 代码块 |
|---|
ListNode* reverseList(ListNode* head) {
if(!head || !(head->next)) {
return head;
}
ListNode *pre = head;
ListNode *p = head->next;
ListNode *next = NULL;
while(p) {
next = p->next;
p->next = pre;
pre = p;
p = next;
}
head->next = nullptr;
return pre;
} |
使用递归收集与root距离为d的结点
void inorder(TreeNode *root) {
stack<TreeNode*> stk;
TreeNode *cur = root;
while(cur || !stk.empty()) {
while(cur) {
stk.push(cur);
cur = cur->left;
}
cur = stk.top();
stk.pop();
cout << cur->val << " ";
cur = cur->right;
}
}
void postorder(TreeNode *root) {
stack<TreeNode*> stk;
TreeNode *cur = root;
TreeNode *prev = nullptr;
while(cur || !stk.empty()) {
while(cur) {
stk.push(cur);
cur = cur->left;
}
cur = stk.top();
if(cur->right && cur->right != prev) {
cur = cur->right;
} else {
stk.pop();
cout << cur->val << " ";
prev = cur;
cur = nullptr;
}
}
} |
层次遍历
| 代码块 |
|---|
void levelorder(TreeNode *root) {
if(!root) return;
queue<TreeNode*> q;
q.push(root);
while(!q.empty()) {
int size = q.size();
for(int i = 0; i < size; i++) {
TreeNode *node = q.front();
q.pop();
cout << node->val << " ";
if(node->left) {
q.push(node->left);
}
if(node->right) {
q.push(node->right);
}
}
} |
| 代码块 |
void collect(TreeNode *root, int d) {
if(root == nullptr || d < 0) {
return;
}
if(d == 0) {
ans.push_back(root->val);
}
collect(root->left, d - 1);
collect(root->right, d - 1);
} |
| 目录 |
|---|