算法练习之leetcode系列1-3

 

1.Reverse Words in a String

public class Solution {
    public String reverseWords(String s) {
        String result[] = s.trim().split(" +");
        String reverseResult[] = new String[result.length];
        String reverse = "";
        if(result.length>0){
        for(int i = 0;i<result.length;i++){
            reverseResult[i] = result[result.length-1-i].trim();
            reverse += reverseResult[i].trim()+" ";
        }
        }
        return reverse.trim();
    }
}

 

 

2.Evaluate Reverse Polish Notation

public class Solution {
public int evalRPN(String[] tokens) {
            List<String> numList = new ArrayList<String>();
            for(int i = 0;i<tokens.length;i++){
                if(tokens[i].equals("+")){
                    String newNum = String.valueOf(Integer.valueOf(numList.get(numList.size()-2))+Integer.valueOf(numList.get(numList.size()-1)));
                    numList.remove(numList.size()-2);
                    numList.remove(numList.size()-1);
                    numList.add(newNum);
                }else if(tokens[i].equals("-")){
                    String newNum = String.valueOf(Integer.valueOf(numList.get(numList.size()-2))-Integer.valueOf(numList.get(numList.size()-1)));                    
                    numList.remove(numList.size()-2);
                    numList.remove(numList.size()-1);
                    numList.add(newNum);
                }else if(tokens[i].equals("*")){
                    String newNum = String.valueOf(Integer.valueOf(numList.get(numList.size()-2))*Integer.valueOf(numList.get(numList.size()-1)));
                    numList.remove(numList.size()-2);
                    numList.remove(numList.size()-1);
                    numList.add(newNum);
                }else if(tokens[i].equals("/")){
                    String newNum = String.valueOf(Integer.valueOf(numList.get(numList.size()-2))/Integer.valueOf(numList.get(numList.size()-1)));
                    numList.remove(numList.size()-2);
                    numList.remove(numList.size()-1);
                    numList.add(newNum);
                }else{
                    numList.add(tokens[i]);
                } 
                    
            }
            return Integer.valueOf(numList.get(0));
                
            }
             
}

3.Max Points on a Line(这个题真是很蛋疼啊，开始时真没想到还会包括出现重复点的情况，导致后来写的有点晕了=.=)

/**
 * Definition for a point.
 * class Point {
 *     int x;
 *     int y;
 *     Point() { x = 0; y = 0; }
 *     Point(int a, int b) { x = a; y = b; }
 * }
 */
public class Solution {
    public int maxPoints(Point[] points) {
        
        List<Integer> numlist = new ArrayList<Integer>();
        HashMap<String, Integer> map;
        HashMap<String, Integer> mapPoint;
        Integer max = 0;
        if (points.length == 1) {
            max = 1;
        }
        for (int i = 0; i < points.length; i++) {
            map = new HashMap<String, Integer>();
            mapPoint = new HashMap<String, Integer>();
            for (int j = i + 1; j < points.length; j++) {
                String kString = "";
                if ((points[i].x - points[j].x) != 0) {
            if (points[i].y - points[j].y == 0) {
                        kString = String.valueOf(0);
                    } else {
                        float k = (float) (points[i].y - points[j].y)
                                / (float) (points[i].x - points[j].x);
                        kString = String.valueOf(k);
                    }
                    if (map.containsKey(kString)) {
                        int num = map.get(kString) + 1;
                        map.remove(kString);
                        map.put(kString, num);
                    } else {
                        map.put(kString, 2);
                    }
                } else if ((points[i].y - points[j].y) != 0
                        && (points[i].x - points[j].x) == 0) {
                    kString = "no";
                    if (map.containsKey(kString)) {
                        int num = map.get(kString) + 1;
                        map.remove(kString);
                        map.put(kString, num);
                    } else {
                        map.put(kString, 2);
                    }
                } else {
                    kString = "re";
                    if (mapPoint.containsKey(kString)) {
                        int num = mapPoint.get(kString) + 1;
                        mapPoint.remove(kString);
                        mapPoint.put(kString, num);
                    } else {
                        mapPoint.put(kString, 2);
                    }
                }

            }
            if (!map.isEmpty()) {
                for (String key : map.keySet()) {
                    if (mapPoint.containsKey("re")
                            && map.get(key) + mapPoint.get("re")
                                    - 1 > max){
                        max = map.get(key) + mapPoint.get("re")
                                - 1;
                    } else if (map.get(key) > max) {
                        max = map.get(key);
                    }

                }
            }
            else {
                if (mapPoint.containsKey("re")
                        && mapPoint.get("re") > max) {
                    max = mapPoint.get("re");
                }
            }
        }

        return max;

    }
}