leetcode热题100道-day1

爬楼梯

class Solution { public int climbStairs(int n) { int[] dp = new int[n + 1]; dp[0] = 1; dp[1] = 1; for(int i = 2; i <= n; i++) { dp[i] = dp[i - 1] + dp[i - 2]; } return dp[n]; } }

合并区间

class Solution { public int[][] merge(int[][] intervals) { if (intervals.length == 0) { return new int[0][2]; } Arrays.sort(intervals, new Comparator<int[]>() { public int compare(int[] interval1, int[] interval2) { return interval1[0] - interval2[0]; } }); List<int[]> merged = new ArrayList<int[]>(); for (int i = 0; i < intervals.length; ++i) { int L = intervals[i][0], R = intervals[i][1]; if (merged.size() == 0 || merged.get(merged.size() - 1)[1] < L) { merged.add(new int[]{L, R}); } else { merged.get(merged.size() - 1)[1] = Math.max(merged.get(merged.size() - 1)[1], R); } } return merged.toArray(new int[merged.size()][]); } }

子集

class Solution { public List<List<Integer>> subsets(int[] nums) { List<List<Integer>> res = new ArrayList<>(); backtrack(0, nums, res, new ArrayList<Integer>()); return res; }