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baiduoa.java
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43 lines (40 loc) · 1.17 KB
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import java.util.*;
public class baiduoa {
/*
1-n 有多少个不上升序列，有多少个不下降序列
* */
static int res;
static Map<String, Integer> map = new HashMap<>();
public static void main(String[] args){
res = 0;
int n = 3;
int[] nums = new int[n];
for(int i=0; i < n; i++){
nums[i] = i+1;
}
dfs(0, 0, "", nums);
System.out.println(res);
System.out.println(mmdfs(0,0,nums));
}
public static void dfs(int level, int index, String path, int[] nums){
if(level == nums.length){
res ++;
System.out.println(path);
return;
}
for(int i = index; i < nums.length; i++){
dfs(level+1, i, path+nums[i], nums);
}
}
// method2: memorized dfs
public static int mmdfs(int level, int index, int[] nums){
String key = level+","+index;
if(map.containsKey(key)) return map.get(key);
if(level == nums.length) return 1;
int sum = 0;
for(int i = index; i < nums.length; i++){
sum += mmdfs(level+1, i, nums);
}
return sum;
}
}