{"trustable":false,"sections":[{"title":"","value":{"format":"HTML","content":"\n \u003cdiv class\u003d\"ptx\" lang\u003d\"en-US\"\u003e\n 有一段从1到n的区间,现有多条线段(左右界不同,有重合区域),求最少需几条线段才能覆盖整个大区间?\n \u003c/div\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\n \u003cdiv class\u003d\"ptx\" lang\u003d\"en-US\"\u003e\n * Line 1: N 和 T \n \u003cbr\u003e \n \u003cbr\u003e* Lines 2..N+1: 区间左右界\n \u003c/div\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\n \u003cdiv class\u003d\"ptx\" lang\u003d\"en-US\"\u003e\n * Line 1: ans or -1\n \u003c/div\u003e"}},{"title":"Sample Input","value":{"format":"HTML","content":"\u003cpre class\u003d\"sio\"\u003e3 10\n1 7\n3 6\n6 10\u003c/pre\u003e"}},{"title":"Sample Output","value":{"format":"HTML","content":"\u003cpre class\u003d\"sio\"\u003e2\u003c/pre\u003e"}},{"title":"Hint","value":{"format":"HTML","content":"\n \u003cdiv class\u003d\"ptx\" lang\u003d\"en-US\"\u003e\n [1, 3],[4, 7]也算覆盖了[1,7]\n \u003c/div\u003e"}}]}