*[Lintcode]Interval Minimum Number 区间最小数

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Given an integer array (index from 0 to n-1, where n is the size of this array), and an query list. Each query has two integers [start, end]. For each query, calculate the minimum number between index start and end in the given array, return the result list.

Example

For array [1,2,7,8,5], and queries [(1,2),(0,4),(2,4)], return [2,1,5]

用线段树直接求解即可。

/** * Definition of Interval: * public classs Interval { *     int start, end; *     Interval(int start, int end) { *         this.start = start; *         this.end = end; *     } */public class Solution {    /**     *@param A, queries: Given an integer array and an query list     *@return: The result list     */    public ArrayList<Integer> intervalMinNumber(int[] A,                                                 ArrayList<Interval> queries) {        SegmentTreeNode s = build(A, 0, A.length - 1);        ArrayList<Integer> res = new ArrayList<Integer>();        for(int i = 0; i < queries.size(); i++) {            Interval interval = queries.get(i);            res.add(find(s, interval));        }        return res;    }        private int find(SegmentTreeNode s, Interval i) {        if(s == null) return Integer.MAX_VALUE;        if(i.start > s.end || i.end < s.start) return Integer.MAX_VALUE;        if(i.start <= s.start && i.end >= s.end) return s.min;        else {            int left = find(s.left, i);            int right = find(s.right, i);            return Math.min(left, right);        }    }        private SegmentTreeNode build(int[] A, int start, int end) {        if(start > end) return null;                SegmentTreeNode root = new SegmentTreeNode(start, end);        if(start == end) {            root.min = A[start];            return root;        }                root.left = build(A, start, (start + end) / 2);        root.right = build(A, (start + end) / 2 + 1, end);                root.min = Math.min(root.left.min, root.right.min);        return root;    }        class SegmentTreeNode {        public int start, end, min;        public SegmentTreeNode left, right;        public SegmentTreeNode(int start, int end) {          this.start = start;          this.end = end;          this.left = this.right = null;      }  } }

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