1.快速幂

public static long qmi(long a, long b, long p) {long r = 1;while (b != 0) {if ((b & 1) == 1) {r = (r * a) % p;}b >>= 1;a = a * a % p;}return r;}

2.Java日期类

日期问题暂更

3.日期问题模板

考前更新

4.状态机DP

1.松散子序列 - 蓝桥云课 (lanqiao.cn)

import java.util.Scanner;public class 松散子序列 {static int N=1000010;static int[][]f=new int[N][2];public static void main(String[] args) {Scanner sc=new Scanner(System.in);String s = sc.next();int n=s.length();s=' '+s;for (int i = 1; i <=n ; i++) {f[i][1]=f[i-1][0]+s.charAt(i)-96;f[i][0]=Math.max(f[i-1][0],f[i-1][1]);}System.out.println(Math.max(f[n][0],f[n][1]));}
}

5.多重背包

1371. 货币系统 - AcWing题库

import java.util.Scanner;public class Main {//f[i][j]=f[i-1][j]+f[i-1][j-v[i]]+f[i-1][j-2*v[i]]+...
//f[i][j-v[i]=f[i-1][j-v[i]]static int N = 30, M = 10010;static int n, m;static long[][] f = new long[N][M];static long[] v = new long[N];public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();int m = sc.nextInt();for (int i = 1; i <= n; i++) {v[i] = sc.nextLong();}for (int i = 0; i <= n; i++)f[i][0] = 1;for (int i = 1; i <= n; i++) {for (int j = 0; j <= m; j++) {f[i][j]=f[i-1][j];if(j>=v[i]) {f[i][j]+=f[i][(int) (j-v[i])];}}}System.out.println(f[n][m]);}
}

重点掌握多重背包的优化；

6.Floyd算法

void floyd()
{for (int k = 1; k <= n; k ++ )for (int i = 1; i <= n; i ++ )for (int j = 1; j <= n; j ++ )d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
}

7.区间合并

给定 n 个区间 [li,ri]]，要求合并所有有交集的区间。

注意如果在端点处相交，也算有交集。

输出合并完成后的区间个数。

例如：[1,3] 和 [2,6] 可以合并为一个区间 [1,6]。

输入格式

第一行包含整数 n。

接下来 n 行，每行包含两个整数 l 和 r。

输出格式

共一行，包含一个整数，表示合并区间完成后的区间个数。

import java.util.Arrays;
import java.util.Scanner;public class Main {static int N=100010;static Node[]A=new Node[N];public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n=sc.nextInt();for(int i=0;i<n;i++) {int l=sc.nextInt();int r=sc.nextInt();A[i]=new Node(l,r);}Arrays.sort(A,0,n);int start=A[0].l,end=A[0].r;int res=1;for(int i=1;i<n;i++) {if(A[i].l<=end) {end=Math.max(end, A[i].r);}else {res++;start=A[i].l;end=A[i].r;}}System.out.println(res);}static class Node implements Comparable<Node>{int l;int r;public Node(int l, int r) {super();this.l = l;this.r = r;}@Overridepublic int compareTo(Node o) {// TODO Auto-generated method stubreturn this.l-o.l;}}}

 8.优先队列贪心问题

1.最大开支 - 蓝桥云课 (lanqiao.cn)

import java.util.PriorityQueue;
import java.util.Scanner;public class 最大开支 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);PriorityQueue<Node> pq = new PriorityQueue<Node>();int n = sc.nextInt();int m = sc.nextInt();long sum = 0;for (int i = 0; i < m; i++) {int k = sc.nextInt();int b = sc.nextInt();if (k + b < 0)continue;pq.offer(new Node(k, b, 1, k+b));}for (int i = 1; i <= n; i++) {if (pq.peek().c > 0) {Node t = pq.poll();sum += t.c;int c = 2 * t.k * t.x + t.k + t.b;int x = t.x + 1;if (t.c > 0) {pq.offer(new Node(t.k, t.b, x, c));}}else {break;}}System.out.println(sum);}static class Node implements Comparable<Node> {int k;int b;int x;int c;public Node(int k, int b, int x, int c) {super();this.k = k;this.b = b;this.x = x;this.c = c;}@Overridepublic int compareTo(Node o) {// TODO Auto-generated method stubreturn o.c - this.c;}}}

9.路径

3.路径 - 蓝桥云课 (lanqiao.cn)

import java.util.Arrays;public class 路径 {static int N = 3000,n,m,k,INF = 0x3f3f3f3f;static int[][] g = new int[N][N];static int[] dist = new int[N];static boolean[] st = new boolean[N];public static void main(String[] args) {for (int i = 1; i <= 2021; i++) {for (int j = 1; j <= 2021; j++) {if (i == j)g[i][j] = 0;else if (Math.abs(i - j) > 21)g[i][j] = INF;else if (Math.abs(i - j) <= 21)g[i][j] = lcm(i, j);}}System.out.println(dijkstra());}public static int dijkstra() {n=2021;Arrays.fill(dist, INF);dist[1] = 0;for (int i = 0; i <n; i++) {int t = -1;for (int j = 1; j <=n; j++) {if (!st[j] && ((t == -1) || dist[j] < dist[t])) {t = j;}}st[t] = true;for (int j = 1; j <=n; j++) {dist[j] = Math.min(dist[j], dist[t] + g[t][j]);}}if(dist[n]==INF)return -1;else return dist[n];}public static int gcd(int a, int b) {return b != 0 ? gcd(b, a % b):a;}public static int lcm(int a, int b) {return a * b / gcd(a, b);}}

10.双指针

1.完全二叉树的权值 - 蓝桥云课 (lanqiao.cn)

import java.util.Scanner;public class 完全二叉树的权值 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();int[] a = new int[n + 1];for (int i = 1; i <= n; i++) {a[i] = sc.nextInt();}int max = Integer.MIN_VALUE;int index = 0;for (int k = 1, i = 1; i <= n; i *= 2, k++) {long sum = 0;for (int j = i; j < i+Math.pow(2, k - 1)&&j<=n; j++) {sum += a[j];}if (sum > max) {max=(int) sum;index = k;}}System.out.println(index);}
}