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Commit d0d7673

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20190409
1 parent 71a611a commit d0d7673

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2 files changed

+58
-4
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2 files changed

+58
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‎code/lc51.java

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package code;
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/*
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* 51. N-Queens
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* 题意:8皇后问题
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* 难度:Hard
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* 分类:Backtracking
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* 思路:回溯+判断,注意怎么判断两个斜线方向
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* Tips:
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*/
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.List;
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public class lc51 {
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StringBuilder ss = new StringBuilder();
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HashSet<String> hs = new HashSet();
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public List<List<String>> solveNQueens(int n) {
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for (int i = 0; i < n-1 ; i++) {
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ss.append(".");
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}
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return dfs(new ArrayList<>(), new ArrayList(), n, 0);
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}
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public List<List<String>> dfs(List<List<String>> res, List curr, int n, int row){
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if(row==n){
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res.add(new ArrayList<>(curr));
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return res;
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}
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for (int i = 0; i < n ; i++) {
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if(isValid(row, i)){
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curr.add(new StringBuilder(ss).insert(i,"Q").toString());
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int a = row+i; // row+col 作为key
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int b = row-i; // row-col 作为key
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hs.add("row"+row); hs.add("col"+i); hs.add("k1"+a); hs.add("k2"+b);
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dfs(res, curr, n, row+1);
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curr.remove(curr.size()-1);
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hs.remove("row"+row); hs.remove("col"+i); hs.remove("k1"+a); hs.remove("k2"+b); //别忘了删掉
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}
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}
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return res;
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}
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public boolean isValid(int row, int col){
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int a = row+col;
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int b = row-col;
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if(hs.contains("row"+row)||hs.contains("col"+col)||hs.contains("k1"+a)||hs.contains("k2"+b)) return false;
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return true;
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}
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}

‎readme.md

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@@ -35,10 +35,10 @@ LeetCode 指南
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| 009 [Java](./code/lc9.java)
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| 010 [Java](./code/lc10.java)
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| 011 [Java](./code/lc11.java)
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| 013 [Java](./code/lc13java)
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| 014 [Java](./code/lc14java)
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| 015 [Java](./code/lc15java)
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| 016 [Java](./code/lc16java)
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| 013 [Java](./code/lc13.java)
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| 014 [Java](./code/lc14.java)
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| 015 [Java](./code/lc15.java)
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| 016 [Java](./code/lc16.java)
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| 017 [Java](./code/lc17.java)
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| 019 [Java](./code/lc19.java)
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| 020 [Java](./code/lc20.java)
@@ -66,6 +66,7 @@ LeetCode 指南
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| 048 [Java](./code/lc48.java)
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| 049 [Java](./code/lc49.java)
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| 050 [Java](./code/lc50.java)
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| 051 [Java](./code/lc51.java)
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| 053 [Java](./code/lc53.java)
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| 054 [Java](./code/lc54.java)
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| 055 [Java](./code/lc55.java)
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| 746 [Java](./code/lc746.java)
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| 771 [Java](./code/lc771.java)
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| 877 [Java](./code/lc877.java)
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| 921 [Java](./code/lc921.java)
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| 922 [Java](./code/lc922.java)
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| 923 [Java](./code/lc923.java)
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| 978 [Java](./code/lc978.java)
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| 983 [Java](./code/lc983.java)

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