1+ package weekly ;
2+
3+ import java .util .ArrayList ;
4+ import java .util .Arrays ;
5+ import java .util .HashMap ;
6+ import java .util .HashSet ;
7+ import java .util .LinkedList ;
8+ import java .util .List ;
9+ import java .util .Map ;
10+ import java .util .Queue ;
11+ import java .util .Set ;
12+
13+ public class wk305 {
14+ //ranking: 903 / 7465
15+
16+ //简单题，遍历即可
17+ public int arithmeticTriplets (int [] nums , int diff ) {
18+ int ans = 0 ;
19+ for (int i = 0 ; i < nums .length ; i ++) {
20+ for (int j = i + 1 ; j < nums .length ; j ++) {
21+ for (int k = j + 1 ; k < nums .length ; k ++) {
22+ if (nums [j ] - nums [i ] == diff && nums [k ] - nums [j ] == diff ) {
23+ ans ++;
24+ }
25+ }
26+ }
27+ }
28+ return ans ;
29+ }
30+
31+
32+ //中等题，bfs+限制
33+ public int reachableNodes (int n , int [][] edges , int [] restricted ) {
34+ Map <Integer , List <Integer >> map = new HashMap <>();
35+ for (int [] edge : edges ) {
36+ if (!map .containsKey (edge [0 ])) map .put (edge [0 ], new ArrayList <>());
37+ if (!map .containsKey (edge [1 ])) map .put (edge [1 ], new ArrayList <>());
38+ map .get (edge [0 ]).add (edge [1 ]);
39+ map .get (edge [1 ]).add (edge [0 ]);
40+ }
41+
42+ Set <Integer > set = new HashSet <>();
43+ for (int i : restricted ) {
44+ set .add (i );
45+ }
46+
47+ Queue <Integer > queue = new LinkedList <>();
48+ queue .add (0 );
49+ int ans = 1 ;
50+ boolean [] visited = new boolean [n ];
51+ visited [0 ] = true ;
52+
53+ while (!queue .isEmpty ()) {
54+ Integer poll = queue .poll ();
55+ for (Integer next : map .getOrDefault (poll , new ArrayList <>())) {
56+ if (visited [next ] || set .contains (next )) continue ;
57+ visited [next ] = true ;
58+ queue .add (next );
59+ ans ++;
60+ }
61+ }
62+ return ans ;
63+
64+ }
65+
66+ /* public boolean validPartition(int[] nums) {
67+ memo = new int[nums.length];
68+ return help(nums, 0);
69+ }
70+
71+ int[] memo;
72+
73+ boolean help(int[] nums, int index) {
74+ if (index >= nums.length) return true;
75+
76+ if (memo[index] != 0) {
77+ return memo[index] == 1;
78+ }
79+ int end = index + 1;
80+ boolean a = false, b = false, c = false;
81+ if (end < nums.length && nums[index] == nums[end]) {
82+ a = help(nums, end + 1);
83+ }
84+ end++;
85+ if (end < nums.length && nums[index] == nums[index + 1] && nums[index + 1] == nums[end]) {
86+ b = help(nums, end + 1);
87+ }
88+ if (end < nums.length && nums[index] + 1 == nums[index + 1] && nums[index + 1] + 1 == nums[end]) {
89+ c = help(nums, end + 1);
90+ }
91+ boolean res = a | b | c;
92+ if (res) {
93+ memo[index] = 1;
94+ } else {
95+ memo[index] = -1;
96+ }
97+ return res;
98+ }*/
99+
100+ //中等题，暴力dp，不要想什么贪心做发 - -！
101+ public boolean validPartition (int [] nums ) {
102+ boolean [] dp = new boolean [nums .length + 1 ];
103+ dp [0 ] = true ;
104+ for (int i = 0 ; i < nums .length ; i ++) {
105+ int start = i - 1 ;
106+ if (start < 0 ) continue ;
107+ if (nums [start ] == nums [i ]) {//两个相同
108+ dp [i + 1 ] |= dp [start ];
109+ }
110+ start --;
111+ if (start < 0 ) continue ;
112+ if (nums [start ] == nums [i - 1 ] && nums [start ] == nums [i ]) {//三个相同
113+ dp [i + 1 ] |= dp [start ];
114+ }
115+ if (nums [start ] + 1 == nums [i - 1 ] && nums [i - 1 ] + 1 == nums [i ]) {//三个相差1
116+ dp [i + 1 ] |= dp [start ];
117+ }
118+ }
119+ return dp [nums .length ];
120+ }
121+
122+ //中等题，直接一维dp
123+ public int longestIdealString (String s , int k ) {
124+ char [] chars = s .toCharArray ();
125+ int [] dp = new int [s .length ()];
126+ int [] index = new int [26 ];//记录字母的位置
127+ Arrays .fill (index , -1 );//初试为-1都不存在
128+ int max = 0 ;
129+ for (int i = 0 ; i < chars .length ; i ++) {
130+ char num = chars [i ];
131+ dp [i ] = 1 ;
132+ //j表示相差k的字母
133+ for (int j = Math .max (0 , num - 'a' - k ); j <= Math .min (25 , num - 'a' + k ); j ++) {
134+ if (index [j ] < 0 ) continue ;
135+ //更新dp[i], 可到达的字母+1
136+ dp [i ] = Math .max (dp [index [j ]] + 1 , dp [i ]);//
137+ }
138+ index [num - 'a' ] = i ;
139+ max = Math .max (max , dp [i ]);
140+ }
141+ return max ;
142+ }
143+
144+ //或者直接dp[26]
145+ /* public int longestIdealString(String s, int k) {
146+ char[] chars = s.toCharArray();
147+ int[] dp = new int[26];
148+ int max = 0;
149+ for (int i = 0; i < chars.length; i++) {
150+ char num = chars[i];
151+ //j表示相差k的字母
152+ for (int j = Math.max(0, num - 'a' - k); j <= Math.min(25, num - 'a' + k); j++) {
153+ dp[num-'a'] = Math.max(dp[j], dp[num-'a']);
154+ }
155+ dp[num-'a'] ++;
156+ max = Math.max(max, dp[i]);
157+ }
158+ return max;
159+
160+ }*/
161+ }
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