leetcode-java/src/ValidTriangleNumber611.java at master · fluency03/leetcode-java · GitHub

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/**
 * Given an array consists of non-negative integers, your task is to count the
 * number of triplets chosen from the array that can make triangles if we take
 * them as side lengths of a triangle.
 *
 * Example 1:
 * Input: [2,2,3,4]
 * Output: 3
 * Explanation:
 * Valid combinations are:
 * 2,3,4 (using the first 2)
 * 2,3,4 (using the second 2)
 * 2,2,3
 *
 * Note:
 * The length of the given array won't exceed 1000.
 * The integers in the given array are in the range of [0, 1000].
 */


publicclassValidTriangleNumber611 {
publicinttriangleNumber(int[] nums) {
if (nums == null || nums.length < 3) return0;
Arrays.sort(nums);
intres = 0;
for (inti=0; i<nums.length-2; i++) {
for (intj=i+1; j<nums.length-1; j++) {
for (intk=j+1; k<nums.length; k++) {
if (isValidTriangle(nums[i], nums[j], nums[k])) res++;
elsebreak;
 }
 }
 }

returnres;
 }

publicbooleanisValidTriangle(inta, intb, intc) {
if (a == 0 || b == 0 || c == 0) returnfalse;
intlongestSide = a;
if (b > longestSide) longestSide = b;
if (c > longestSide) longestSide = c;
returnlongestSide < (a + b + c - longestSide);
 }


publicinttriangleNumber2(int[] nums) {
if (nums == null || nums.length < 3) return0;

Arrays.sort(nums);
int[] sum = newint[1001];
for(intn: nums) sum[n]++;
for(inti=1; i<1001; i++) sum[i] += sum[i-1];

intres = 0;
for (inti=0; i<nums.length-2; i++) {
if (nums[i] == 0) continue;
for (intj=i+1; j<nums.length-1; j++) {
if (nums[j] == 0) continue;
intupper = nums[i] + nums[j];
intlower = Math.abs(nums[i] - nums[j]);
intc = sum[upper-1] - Math.max(sum[lower], j+1);
res += c;
 }
 }
returnres;
 }

/**
 * https://leetcode.com/problems/valid-triangle-number/solution/
 */
publicinttriangleNumber3(int[] nums) {
intcount = 0;
Arrays.sort(nums);
for (inti = 0; i < nums.length - 2; i++) {
intk = i + 2;
for (intj = i + 1; j < nums.length - 1 && nums[i] != 0; j++) {
while (k < nums.length && nums[i] + nums[j] > nums[k])
k++;
count += k - j - 1;
 }
 }
returncount;
 }

/**
 * https://leetcode.com/problems/valid-triangle-number/discuss/104174/Java-O(n2)-Time-O(1)-Space
 */
publicstaticinttriangleNumber4(int[] A) {
Arrays.sort(A);
intcount = 0, n = A.length;
for (inti=n-1;i>=2;i--) {
intl = 0, r = i-1;
while (l < r) {
if (A[l] + A[r] > A[i]) {
count += r-l;
r--;
 }
elsel++;
 }
 }
returncount;
 }

}