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LeetCode40.java
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69 lines (64 loc) · 2.3 KB
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package problems;
import java.util.*;
public class LeetCode40 {
public List<List<Integer>> combinationSum2(int[] candidates, int target) {
List<List<Integer>> res = new ArrayList<>();
Deque<Integer> path = new ArrayDeque<>();
int length = candidates.length;
if(length == 0){
return res;
}
// 关键步骤
Arrays.sort(candidates);
backtrack(candidates, 0, length, target, path, res);
return res;
}
private void backtrack(int[] candidates, int begin, int length, int target, Deque<Integer> path, List<List<Integer>> res) {
if(target == 0){
res.add(new ArrayList<>(path));
return;
}
for (int i = begin; i < length; i++) {
// 大剪枝：减去candidate[i] 小于0，减去后面的 candidate[i+1]、candidate[i+2]肯定也小于0，因此用 break;
if(target - candidates[i] < 0){
break;
}
// 小剪枝：同一层相同数值的结点，从第2个开始，候选数更少，因此跳过，用continue
if(i > begin && candidates[i] == candidates[i-1]){
continue;
}
path.add(candidates[i]);
backtrack(candidates, i+1, length, target - candidates[i], path, res);
path.removeLast();
}
}
}
class LeetCode40_1 {
public List<List<Integer>> combinationSum2(int[] candidates, int target) {
Arrays.sort(candidates);
List<List<Integer>> ans = new ArrayList<>();
Deque<Integer> res = new ArrayDeque<>();
dfs(candidates, ans, res, 0, target);
return ans;
}
private void dfs(int[] candidates, List<List<Integer>> ans, Deque<Integer> res, int index, int target) {
if(target < 0) {
return;
}
if(target == 0) {
ans.add(new ArrayList<>(res));
return;
}
for (int i = index; i < candidates.length; i++) {
if(target - candidates[i] < 0) {
break;
}
if(i > index && candidates[i] == candidates[i - 1]) {
continue;
}
res.add(candidates[i]);
dfs(candidates, ans, res, i + 1, target - candidates[i]);
res.removeLast();
}
}
}