leetcode oj java Non-overlapping Intervals

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一、问题描述：

Given a collection of intervals, find the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping.

Note:

You may assume the interval's end point is always bigger than its start point.
Intervals like [1,2] and [2,3] have borders "touching" but they don't overlap each other.

Example 1:

Input: [ [1,2], [2,3], [3,4], [1,3] ]Output: 1Explanation: [1,3] can be removed and the rest of intervals are non-overlapping.

Example 2:

Input: [ [1,2], [1,2], [1,2] ]Output: 2Explanation: You need to remove two [1,2] to make the rest of intervals non-overlapping.

Example 3:

Input: [ [1,2], [2,3] ]Output: 0Explanation: You don't need to remove any of the intervals since they're already non-overlapping.

二、解决思路：

把这些intervals　按照start 从小到大排序，当start相同的时候按照end从小到大排序。

遍历整个数组，如果遇到第i个的end 大于第i+1个的start的时候，为了保证删除的数目最小，每次删除的应该是end较大的，如果第i个的end 大于第i+1个的end, 就把第i个删除。如果第i个的end 小于第i+1个的end, 就把第i+1个删除。

三、代码：

package T12;/** * @author 作者 : xcy * @version 创建时间：2016年12月24日 下午9:34:08 *          类说明 */public class t435 {    public static void main(String[] args) {        // TODO Auto-generated method stub        int[][] re = { { -100, -87 }, { -99, -44 }, { -98, -19 }, { -97, -33 }, { -96, -60 }, { -95, -17 },                { -94, -44 }, { -93, -9 }, { -92, -63 }, { -91, -76 }, { -90, -44 }, { -89, -18 }, { -88, 10 },                { -87, -39 }, { -86, 7 }, { -85, -76 }, { -84, -51 }, { -83, -48 }, { -82, -36 }, { -81, -63 },                { -80, -71 }, { -79, -4 }, { -78, -63 }, { -77, -14 }, { -76, -10 }, { -75, -36 }, { -74, 31 },                { -73, 11 }, { -72, -50 }, { -71, -30 }, { -70, 33 }, { -69, -37 }, { -68, -50 }, { -67, 6 },                { -66, -50 }, { -65, -26 }, { -64, 21 }, { -63, -8 }, { -62, 23 }, { -61, -34 }, { -60, 13 },                { -59, 19 }, { -58, 41 }, { -57, -15 }, { -56, 35 }, { -55, -4 }, { -54, -20 }, { -53, 44 },                { -52, 48 }, { -51, 12 }, { -50, -43 }, { -49, 10 }, { -48, -34 }, { -47, 3 }, { -46, 28 }, { -45, 51 },                { -44, -14 }, { -43, 59 }, { -42, -6 }, { -41, -32 }, { -40, -12 }, { -39, 33 }, { -38, 17 },                { -37, -7 }, { -36, -29 }, { -35, 24 }, { -34, 49 }, { -33, -19 }, { -32, 2 }, { -31, 8 }, { -30, 74 },                { -29, 58 }, { -28, 13 }, { -27, -8 }, { -26, 45 }, { -25, -5 }, { -24, 45 }, { -23, 19 }, { -22, 9 },                { -21, 54 }, { -20, 1 }, { -19, 81 }, { -18, 17 }, { -17, -10 }, { -16, 7 }, { -15, 86 }, { -14, -3 },                { -13, -3 }, { -12, 45 }, { -11, 93 }, { -10, 84 }, { -9, 20 }, { -8, 3 }, { -7, 81 }, { -6, 52 },                { -5, 67 }, { -4, 18 }, { -3, 40 }, { -2, 42 }, { -1, 49 }, { 0, 7 }, { 1, 104 }, { 2, 79 }, { 3, 37 },                { 4, 47 }, { 5, 69 }, { 6, 89 }, { 7, 110 }, { 8, 108 }, { 9, 19 }, { 10, 25 }, { 11, 48 }, { 12, 63 },                { 13, 94 }, { 14, 55 }, { 15, 119 }, { 16, 64 }, { 17, 122 }, { 18, 92 }, { 19, 37 }, { 20, 86 },                { 21, 84 }, { 22, 122 }, { 23, 37 }, { 24, 125 }, { 25, 99 }, { 26, 45 }, { 27, 63 }, { 28, 40 },                { 29, 97 }, { 30, 78 }, { 31, 102 }, { 32, 120 }, { 33, 91 }, { 34, 107 }, { 35, 62 }, { 36, 137 },                { 37, 55 }, { 38, 115 }, { 39, 46 }, { 40, 136 }, { 41, 78 }, { 42, 86 }, { 43, 106 }, { 44, 66 },                { 45, 141 }, { 46, 92 }, { 47, 132 }, { 48, 89 }, { 49, 61 }, { 50, 128 }, { 51, 155 }, { 52, 153 },                { 53, 78 }, { 54, 114 }, { 55, 84 }, { 56, 151 }, { 57, 123 }, { 58, 69 }, { 59, 91 }, { 60, 89 },                { 61, 73 }, { 62, 81 }, { 63, 139 }, { 64, 108 }, { 65, 165 }, { 66, 92 }, { 67, 117 }, { 68, 140 },                { 69, 109 }, { 70, 102 }, { 71, 171 }, { 72, 141 }, { 73, 117 }, { 74, 124 }, { 75, 171 }, { 76, 132 },                { 77, 142 }, { 78, 107 }, { 79, 132 }, { 80, 171 }, { 81, 104 }, { 82, 160 }, { 83, 128 }, { 84, 137 },                { 85, 176 }, { 86, 188 }, { 87, 178 }, { 88, 117 }, { 89, 115 }, { 90, 140 }, { 91, 165 }, { 92, 133 },                { 93, 114 }, { 94, 125 }, { 95, 135 }, { 96, 144 }, { 97, 114 }, { 98, 183 }, { 99, 157 } };        Interval[] intervals = new Interval[re.length];        for (int i = 0; i < re.length; i++) {            intervals[i] = new Interval(re[i][0], re[i][1]);        }        System.out.println(eraseOverlapIntervals(intervals));    }    public static int eraseOverlapIntervals(Interval[] intervals) {        int MIN = -1000;        int n = intervals.length;        if (n < 2) {            return 0;        }        // 先sort  按照start sort , 如果start 相同，那么按照end sort.        boolean flag = true;        for (int i = 0; i < n - 1; i++) {            flag = false;            for (int j = n - 1; j > i; j--) {                if (intervals[j].start < intervals[j - 1].start) {                    Interval tmp = intervals[j];                    intervals[j] = intervals[j - 1];                    intervals[j - 1] = tmp;                    flag = true;                }            }            if (!flag) {                break;            }        }        for (int i = 0; i < n - 1; i++) {            if (intervals[i].start == intervals[i + 1].start) {                if (intervals[i].end > intervals[i + 1].end) {                    Interval tmp = intervals[i];                    intervals[i] = intervals[i + 1];                    intervals[i + 1] = tmp;                }            }        }        int re = 0;        int j = 0;        for (int i = 0; i < n - 1; i++) {            j = i + 1;            while (j < n && intervals[i].end > intervals[j].start) {                if (intervals[i].end > intervals[j].end) {                    re++;                    intervals[i] = new Interval(MIN, MIN);                    break;                } else {                    re++;                    intervals[j] = new Interval(MIN, MIN);                }                j++;            }        }        return re;    }}

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