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Commit 9e6859a

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20190507
1 parent 15e0467 commit 9e6859a

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3 files changed

+82
-1
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3 files changed

+82
-1
lines changed

‎code/lc343.java

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package code;
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/*
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* 343. Integer Break
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* 题意:给定一个正整数,找出一组数字和为该数,且这组数的乘积最大
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* 难度:Medium
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* 分类:Math, Dynamic Programming
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* 思路:能减3的减3,因为3得到的乘积最大
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* Tips:
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*/
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public class lc343 {
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public int integerBreak(int n) {
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if(n==2) return 1;
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if(n==3) return 2;
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return helper(n);
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}
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public int helper(int n){
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if(n==2) return 2;
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if(n==3) return 3;
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if(n==4) return 4;
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if(n==5) return 6;
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else return helper(n-3)*3;
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}
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}

‎code/lc685.java

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package code;
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/*
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* 685. Redundant Connection II
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* 题意:一个图,删掉一个边,使其成为一个根树
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* 难度:Hard
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* 分类:Tree, Depth-first Search, Union Find, Graph
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* 思路:要把问题想清楚
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* 判断是否有某个节点父节点有两个, 记为e1, e2
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* 再判断是否有环
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* 4中情况,分别想清楚返回什么
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* 自己没想清楚两种情况的交叉,以为判断完第一步就可直接返回
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* 如何判断有环,可以利用并查集的思想
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* Tips:https://leetcode.com/problems/redundant-connection-ii/discuss/108045/C%2B%2BJava-Union-Find-with-explanation-O(n)
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*/
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public class lc685 {
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public int[] findRedundantDirectedConnection(int[][] edges) {
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int[] can1 = {-1, -1};
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int[] can2 = {-1, -1};
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int[] parent = new int[edges.length + 1];
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for (int i = 0; i < edges.length; i++) {
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if (parent[edges[i][1]] == 0) {
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parent[edges[i][1]] = edges[i][0];
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} else {
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can2 = new int[] {edges[i][0], edges[i][1]};
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can1 = new int[] {parent[edges[i][1]], edges[i][1]};
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edges[i][1] = 0;
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}
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}
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for (int i = 0; i < edges.length; i++) {
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parent[i] = i;
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}
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for (int i = 0; i < edges.length; i++) {
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if (edges[i][1] == 0) {
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continue;
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}
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int child = edges[i][1], father = edges[i][0];
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if (root(parent, father) == child) { //判断father的父节点是不是child
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if (can1[0] == -1) {
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return edges[i];
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}
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return can1;
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}
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parent[child] = father;
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}
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return can2;
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}
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int root(int[] parent, int i) {
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while (i != parent[i]) { //找到根为止
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parent[i] = parent[parent[i]];
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i = parent[i];
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}
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return i;
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}
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}

‎readme.md

Lines changed: 3 additions & 1 deletion
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@@ -190,7 +190,8 @@ LeetCode 指南
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| 337 [Java](./code/lc337.java)
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| 338 [Java](./code/lc338.java)
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| 341 [Java](./code/lc341.java)
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| 344 [Java](./code/lc338.java)
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| 343 [Java](./code/lc343.java)
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| 344 [Java](./code/lc344.java)
194195
| 347 [Java](./code/lc347.java)
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| 350 [Java](./code/lc350.java)
196197
| 371 [Java](./code/lc371.java)
@@ -217,6 +218,7 @@ LeetCode 指南
217218
| 617 [Java](./code/lc617.java)
218219
| 621 [Java](./code/lc621.java)
219220
| 647 [Java](./code/lc647.java)
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| 685 [Java](./code/lc685.java)
220222
| 714 [Java](./code/lc714.java)
221223
| 746 [Java](./code/lc746.java)
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| 771 [Java](./code/lc771.java)

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