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Commit 3fe6a59

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新增回溯算法
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13 files changed

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‎README.md‎

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3939
| 55 | [跳跃游戏](https://leetcode-cn.com/problems/jump-game/) | [jump_game](./greed/leetcode/medium/jump_game.h) | <font color=orange> medium </font> | ✅ |
4040
| 56 | [合并区间](https://leetcode-cn.com/problems/merge-intervals/) | [merge_intervals](./sort/leetcode/merge_intervals.h) | <font color=orange> medium </font> | ✅ |
4141
| 58| [最后一个单词的长度](https://leetcode-cn.com/problems/length-of-last-word) | [lengthOfLastWord](./string/leetcode/easy/lengthOfLastWord.h) | <font color=green>easy</font> | ✅ |
42+
| 60 | [第k个排列](https://leetcode-cn.com/problems/permutation-sequence/)| [permutation_sequence](./backtracking/leetcode/medium/permutation_sequence.h) | <font color=orange> medium </font> | ✅|
4243
| 66 | [加一](https://leetcode-cn.com/problems/plus-one/) | [plusOne](./array/leetcode/easy/plusOne.h) | <font color=green>easy</font> | ✅ |
4344
| 67 | [二进制求和](https://leetcode-cn.com/problems/add-binary/) | [addBinary](./array/leetcode/easy/addBinary.h) | <font color=green>easy</font> | ✅ |
4445
| 69 | [x 的平方根](https://leetcode-cn.com/problems/sqrtx/%E2%80%A8)| [mySqrt](./bsearch/leetcode/mySqrt.h) | <font color=green>easy</font> | ✅ |
4546
| 70 | [爬楼梯](https://leetcode-cn.com/problems/climbing-stairs/)| [climbStairs](./dp/leetcode/easy/climbStairs.h) | <font color=green>easy</font> | ✅ |
4647
| 74 | [搜索二维矩阵](https://leetcode-cn.com/problems/search-a-2d-matrix/) | [search_a_2d_matrix](./bsearch/leetcode/medium/search_a_2d_matrix.h) | <font color=orange> medium </font> | ✅ |
4748
| 75 | [颜色分类](https://leetcode-cn.com/problems/sort-colors/) | [sort_colors](./sort/leetcode/sort_colors.h) | <font color=orange> medium </font> | ✅ |
49+
| 77 | [组合](https://leetcode-cn.com/problems/combinations/)| [combinations](./backtracking/leetcode/medium/combinations.h) | <font color=orange> medium </font> | ✅|
50+
| 78 | [子集](https://leetcode-cn.com/problems/subsets/)| [subsets](./backtracking/leetcode/medium/subsets.h) | <font color=orange> medium </font> | ✅|
51+
| 79 | [单词搜索](https://leetcode-cn.com/problems/word-search/)| [word_search](./backtracking/leetcode/medium/word_search.h) | <font color=orange> medium </font> | ✅|
4852
| 81 | [搜索旋转排序数组II](https://leetcode-cn.com/problems/search-in-rotated-sorted-array-ii/) | [searchInRotatedSortedArrayII](./bsearch/leetcode/medium/searchInRotatedSortedArrayII.h) | <font color=orange> medium </font> | ✅ |
4953
| 83 | [删除排序链表中的重复元素](https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list/)| [deleteDuplicates](./linkedList/leetcode/easy/deleteDuplicates.h) | <font color=green>easy</font> | ✅ |
5054
| 88 | [合并两个有序数组](https://leetcode-cn.com/problems/merge-sorted-array/) | [merge](./array/leetcode/easy/merge.h) | <font color=green>easy</font> | ✅ |
55+
| 89 | [格雷编码](https://leetcode-cn.com/problems/gray-code/)| [gray_code](./backtracking/leetcode/medium/gray_code.h) | <font color=orange> medium </font> | ✅|
56+
| 90 | [子集II](https://leetcode-cn.com/problems/subsets-ii)| [subsets_ii](./backtracking/leetcode/medium/subsets_ii.h) | <font color=orange> medium </font> | ✅|
57+
| 93 | [复原IP地址](https://leetcode-cn.com/problems/restore-ip-addresses)| [restore_ip_addresses](./backtracking/leetcode/medium/restore_ip_addresses.h) | <font color=orange> medium </font> | ✅|
5158
| 100 | [相同的树](https://leetcode-cn.com/problems/same-tree/) | [isSameTree](./tree/leetcode/easy/isSameTree.h) | <font color=green>easy</font> | ✅ |
5259
| 134 | [加油站](https://leetcode-cn.com/problems/gas-station/) | [gas_station](./greed/leetcode/medium/gas_station.h) | <font color=orange> medium </font> | ✅ |
5360
| 153 | [寻找旋转排序数组中的最小值](https://leetcode-cn.com/problems/find-minimum-in-rotated-sorted-array/) | [find_minimum_in_rotated_sorted_array](./bsearch/leetcode/medium/find_minimum_in_rotated_sorted_array.h) | <font color=orange> medium </font> | ✅ |

‎alg-cpp.xcodeproj/project.pbxproj‎

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686+
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‎backtracking.md‎

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| 40 | [组合总和II](https://leetcode-cn.com/problems/combination-sum-ii/)| [combinationSumII](./backtracking/leetcode/medium/combinationSumII.h) | <font color=orange> medium </font> | ✅|
2626
| 46 | [全排列](https://leetcode-cn.com/problems/permutations/)| [permutations](./backtracking/leetcode/medium/permutations.h) | <font color=orange> medium </font> | ✅|
2727
| 47 | [全排列II](https://leetcode-cn.com/problems/permutations-ii/)| [permutationsii](./backtracking/leetcode/medium/permutationsii.h) | <font color=orange> medium </font> | ✅|
28-
28+
| 60 | [第k个排列](https://leetcode-cn.com/problems/permutation-sequence/)| [permutation_sequence](./backtracking/leetcode/medium/permutation_sequence.h) | <font color=orange> medium </font> | ✅|
29+
| 77 | [组合](https://leetcode-cn.com/problems/combinations/)| [combinations](./backtracking/leetcode/medium/combinations.h) | <font color=orange> medium </font> | ✅|
30+
| 78 | [子集](https://leetcode-cn.com/problems/subsets/)| [subsets](./backtracking/leetcode/medium/subsets.h) | <font color=orange> medium </font> | ✅|
31+
| 79 | [单词搜索](https://leetcode-cn.com/problems/word-search/)| [word_search](./backtracking/leetcode/medium/word_search.h) | <font color=orange> medium </font> | ✅|
32+
| 89 | [格雷编码](https://leetcode-cn.com/problems/gray-code/)| [gray_code](./backtracking/leetcode/medium/gray_code.h) | <font color=orange> medium </font> | ✅|
33+
| 90 | [子集II](https://leetcode-cn.com/problems/subsets-ii)| [subsets_ii](./backtracking/leetcode/medium/subsets_ii.h) | <font color=orange> medium </font> | ✅|
34+
| 93 | [复原IP地址](https://leetcode-cn.com/problems/restore-ip-addresses)| [restore_ip_addresses](./backtracking/leetcode/medium/restore_ip_addresses.h) | <font color=orange> medium </font> | ✅|
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### 剑指Offer
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| &emsp;题号&emsp; | 题目链接&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;| 答案链接&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;&emsp;| &emsp;难度&emsp; | &emsp;完成度&emsp; |
3137
| :--: | :--: | :----------------------------------------------------------- | :----------------------------------------------------------- | :------: |
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1+
//
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// combinations.h
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// backtracking
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//
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// Created by junl on 2019年9月22日.
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// Copyright © 2019 junl. All rights reserved.
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//
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#ifndef combinations_hpp
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#define combinations_hpp
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#include <stdio.h>
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/*
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给定两个整数 n 和 k,返回 1 ... n 中所有可能的 k 个数的组合。
16+
17+
示例:
18+
19+
输入: n = 4, k = 2
20+
输出:
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[
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[2,4],
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[3,4],
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[2,3],
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[1,2],
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[1,3],
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[1,4],
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]
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来源:力扣(LeetCode)
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链接:https://leetcode-cn.com/problems/combinations
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著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。
33+
*/
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namespace leetcode {
36+
class Solution77 {
37+
public:
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/*
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思路:回溯
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其实这题和全排列思路是一样的,区别在于排列数只有k个数.
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我们把问题的求解分为K个阶段,每个阶段需要从1...n中随机选择一个数,这样K个阶段后,就能求出k个数的组合.
43+
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这种解法效率有点低,看解法2
45+
*/
46+
vector<vector<int>> combine(int n, int k) {
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if (k > n) return {};
48+
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vector<int> elements;
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vector<int> st;
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st.resize(n+1);
52+
vector<vector<int>> results;
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combine(n, k, elements, st, results);
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return results;
55+
}
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void combine(int n, int k, vector<int> elements, vector<int> st, vector<vector<int>>& results){
58+
if (elements.size() == k){
59+
//find
60+
results.push_back(elements);
61+
return;
62+
}
63+
64+
for(int i=1;i<=n;i++){
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if(st[i]) //跳过重复数字
66+
continue;
67+
if(elements.size()>0 && i<= elements.back()){
68+
continue;
69+
}
70+
elements.push_back(i);st[i]=true;
71+
combine(n, k, elements, st, results);
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elements.pop_back();st[i]=false;
73+
}
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}
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77+
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/*
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思路:
80+
利用模式匹配,比如n=5,k=3.构建状态[11100],我们需要将它变换成[00111],即把左边的1依次移动到右边去,每一次移动就是一种排列的可能。
81+
*/
82+
vector<vector<int>> combine2(int n, int k){
83+
if (k > n) return {};
84+
vector<vector<int>> results;
85+
vector<int> st;
86+
for (int i=0; i<n; i++) {
87+
st.push_back(i<k ? 1 : 0);
88+
}
89+
while (true) {
90+
vector<int> temp;
91+
for (int i=0; i<n; i++) {
92+
if (st[i]) {
93+
temp.push_back(i);
94+
}
95+
}
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results.push_back(temp);
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//1.找到10的结构,然后转换为01
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//2.移动右边的1到最左边
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int found = false;
101+
int one_count = 0;
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for (int i=0; i<n-1; i++) {
103+
if (st[i] == 1 && st[i+1] == 0) {
104+
st[i]=0;st[i+1]=1;
105+
found = true;
106+
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for (int j=0; j<i; j++) {
108+
st[j] = one_count-- > 0 ? 1:0;
109+
}
110+
break;
111+
}
112+
if (st[i] == 1){
113+
one_count++;
114+
}
115+
}
116+
if (!found) {
117+
break;
118+
}
119+
}
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121+
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return results;
123+
}
124+
};
125+
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void test_combinations(){
127+
Solution77 solution;
128+
cout << "test_combinations starting ........" << endl;
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auto x = solution.combine(4, 2);
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x;
131+
}
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}
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#endif /* combinations_hpp */
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//
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// gray_code.h
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// backtracking
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//
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// Created by junl on 2019年9月25日.
6+
// Copyright © 2019 junl. All rights reserved.
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//
8+
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#ifndef gray_code_hpp
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#define gray_code_hpp
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#include <stdio.h>
13+
#include <math.h>
14+
/*
15+
89. 格雷编码
16+
格雷编码是一个二进制数字系统,在该系统中,两个连续的数值仅有一个位数的差异。
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给定一个代表编码总位数的非负整数 n,打印其格雷编码序列。格雷编码序列必须以 0 开头。
19+
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示例 1:
21+
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输入: 2
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输出: [0,1,3,2]
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解释:
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00 - 0
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01 - 1
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11 - 3
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10 - 2
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对于给定的 n,其格雷编码序列并不唯一。
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例如,[0,2,3,1] 也是一个有效的格雷编码序列。
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00 - 0
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10 - 2
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11 - 3
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01 - 1
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*/
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namespace leetcode {
40+
class Solution89 {
41+
public:
42+
vector<int> results;
43+
44+
vector<int> grayCode(int n) {
45+
if (n == 0) return {0};
46+
map<string,bool> st;
47+
string elements;
48+
for(int i=0;i<n;i++){
49+
elements+='0';
50+
}
51+
int totalCount = pow(2,n);
52+
grayCode(elements, st, totalCount);
53+
return results;
54+
}
55+
56+
void grayCode(string elements, map<string,bool> &st, int totalCount){
57+
if (results.size() == totalCount || st[elements])
58+
return;
59+
int loc = calc10(elements);
60+
results.push_back(loc);
61+
st[elements] = true;
62+
for(int i=0;i<elements.size();i++){
63+
elements[i] = elements[i] == '0' ? '1' : '0';
64+
grayCode(elements, st, totalCount);
65+
elements[i] = elements[i] == '0' ? '1' : '0';
66+
}
67+
}
68+
69+
int calc10(string &nums){
70+
int sum=0;
71+
int l = 1;
72+
for(int i=nums.size()-1;i>=0;i--){
73+
sum+=(nums[i]-'0')*l;
74+
l*=2;
75+
}
76+
return sum;
77+
}
78+
};
79+
80+
void test_gray_code(){
81+
cout << "test_gray_code starting...." << endl;
82+
Solution89 so;
83+
vector<int> results = so.grayCode(2);
84+
for (auto &i:results){
85+
cout << i << ", ";
86+
}
87+
cout << endl;
88+
}
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}
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#endif /* gray_code_hpp */

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