文档讲解：39. 组合总和、40.组合总和II、131.分割回文串

题目链接：39. 组合总和、40.组合总和II、131.分割回文串

216.组合总和III

class Solution {List<List<Integer>> res = new ArrayList<>();List<Integer> path = new ArrayList<>();public List<List<Integer>> combinationSum(int[] candidates, int target) {Arrays.sort(candidates);int sum=0;backTracking(candidates, target, sum, 0);return res;}public void backTracking(int[] candidates, int target, int sum, int index){if(sum>target){return;}if(sum == target){res.add(new ArrayList<>(path));return;}for(int i=index;i< candidates.length && sum + candidates[i] <= target;++i){path.add(candidates[i]);sum+=candidates[i];backTracking(candidates, target, sum, i);path.remove(path.size()-1);sum-=candidates[i];}}
}

17.电话号码的字母组合

class Solution {List<List<Integer>> res = new ArrayList<>();List<Integer> path = new ArrayList<>();boolean[] used;int sum=0;public List<List<Integer>> combinationSum2(int[] candidates, int target) {used = new boolean[candidates.length];Arrays.fill(used, false);Arrays.sort(candidates);backTracking(candidates, target, 0);return res;}public void backTracking(int[] candidates, int target, int index){if(sum == target){res.add(new ArrayList<>(path));return;}for(int i=index;i<candidates.length; ++i){if (sum + candidates[i] > target) {break;}if(i>0 && candidates[i] == candidates[i-1] && !used[i-1])  continue;            sum+=candidates[i];used[i] = true;path.add(candidates[i]);backTracking(candidates, target, i+1);path.remove(path.size()-1);sum-=candidates[i];used[i] = false;}}
}

131.分割回文串

class Solution {List<List<String>> res = new ArrayList<>();Deque<String> path = new LinkedList<>();public List<List<String>> partition(String s) {backTracing(s, 0);return res;}public void backTracing(String s, int index){if(index >= s.length()){res.add(new ArrayList<>(path));return;}for(int i=index;i<s.length(); i++){if(isPalindrome(s, index, i)){String str = s.substring(index, i+1);path.addLast(str);}else{continue;}backTracing(s, i+1);path.removeLast();}}public boolean isPalindrome(String s, int index, int end){for(int i=index, j=end; i<j; i++, j--){if(s.charAt(i) != s.charAt(j)){return false;}}return true;}
}