Kth Smallest Subarray Sum
找第k小的subarray sum.
这题吧..如果不卡时间, 应该不难, 但是这题用treeset过不了, 所以只能用binary search做, 已知subarray sum可以用pre sum求, 并且是递增的 (nums[i] >= 1) 所以这题可以用binary search找一个mid最小值下, 第k的值.
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class Solution { public int kthSmallestSubarraySum(int[] nums, int k) { int l = 0; int r = Integer.MAX_VALUE; while(l < r) { int m = (l + r) / 2; int f = check(nums, m); if(f < k) l = m + 1; else r = m; } return l; } public int check(int[] nums, int m){ int sum = 0; int i = 0; int j = 0; int res = 0; while(i < nums.length){ if(sum + nums[i] <= m){ sum += nums[i]; i++; res += i - j; } else { sum -= nums[j]; j++; } } return res; } } |
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class Solution { public int kthSmallestSubarraySum(int[] nums, int k) { int n = nums.length; int[] pre = new int[n + 1]; for(int i = 1 ; i <= n; i++) { pre[i] = pre[i - 1] + nums[i - 1]; } LinkedList<Integer> list = new LinkedList<>(); for(int i = 0; i <= n; i++){ for(int j = i + 1; j <= n; j++){ list.add(pre[j] - pre[i]); } } Collections.sort(list); System.out.println(list); while(--k != 0){ list.removeFirst(); } return list.getFirst(); } } |