完成作业

Author: YorkPeng

171.excel表列序号.java

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+import java.util.HashMap;
+import java.util.Map;
+
+/*
+ * @lc app=leetcode.cn id=171 lang=java
+ *
+ * [171] Excel表列序号
+ */
+
+// @lc code=start
+class Solution {
+    public int titleToNumber(String s) {
+ //       Map<String,Integer> map = new HashMap<>();
+ //       map.put("A", 1);
+ //       map.put("B", 2);
+ //       map.put("C", 3);
+ //       map.put("D", 4);
+ //       map.put("E", 5);
+ //       map.put("F", 6);
+ //       map.put("G", 7);
+ //       map.put("H", 8);
+ //       map.put("I", 9);
+ //       map.put("J", 10);
+ //       map.put("K", 11);
+ //       map.put("L", 12);
+ //       map.put("M", 13);
+ //       map.put("N", 14);
+ //       map.put("O", 15);
+ //       map.put("P", 16);
+ //       map.put("Q", 17);
+ //       map.put("R", 18);
+ //       map.put("S", 19);
+ //       map.put("T", 20);
+ //       map.put("U", 21);
+ //       map.put("V", 22);
+ //       map.put("W", 23);
+ //       map.put("X", 24);
+ //       map.put("Y", 25);
+ //       map.put("Z", 26);
+ //       char[] chars = s.toCharArray();
+ //       int count = 0;
+ //       for(int i = 0;i<chars.length;i++){
+ //           count*=26;
+ //           count+=map.get(String.valueOf(chars[i]));
+ //       }
+ //       return count;
+
+        int count = 0;
+        char[] chars = s.toCharArray();
+        for(int i=0;i<chars.length;i++){
+            count = count * 26 + (chars[i] - 'A'+1);
+        }
+        return count ;
+    }
+}
+// @lc code=end
+

278.第一个错误的版本.java

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+/*
+ * @lc app=leetcode.cn id=278 lang=java
+ *
+ * [278] 第一个错误的版本
+ */
+
+// @lc code=start
+/* The isBadVersion API is defined in the parent class VersionControl.
+      boolean isBadVersion(int version); */
+
+public class Solution extends VersionControl {
+    public int firstBadVersion(int n) {
+        int low = 1;
+        int big = n;
+        int mid = low + (big-low)/2;
+        int index = -1;
+        while(low <= big){
+            if(isBadVersion(mid)){
+                big =mid-1;
+                index = mid;
+            }else{
+                low = mid +1;
+            }
+            mid = low + (big - low )/2;
+        }
+        return index;
+        
+    }
+}
+// @lc code=end
+

374.猜数字大小.java

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+/*
+ * @lc app=leetcode.cn id=374 lang=java
+ *
+ * [374] 猜数字大小
+ */
+
+// @lc code=start
+/** 
+ * Forward declaration of guess API.
+ * @param  num   your guess
+ * @return 	     -1 if num is lower than the guess number
+ *			      1 if num is higher than the guess number
+ *               otherwise return 0
+ * int guess(int num);
+ */
+
+public class Solution extends GuessGame {
+    public int guessNumber(int n) {
+        int half = 1 + (n-1)/2;
+        int low = 1;
+        int big = n;
+        int result = 0;
+        while(low <= big){
+            result = guess(half);
+            if(result == -1){
+                big = half-1;
+                half = low + (big - low)/2;
+            }else if(result == 1){
+                low = half +1;
+                half = low +(big-low)/2;
+            }else{
+                return half;
+            }
+        }
+        return 1;
+    }
+}
+// @lc code=end
+

605.种花问题.java

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+/*
+ * @lc app=leetcode.cn id=605 lang=java
+ *
+ * [605] 种花问题
+ */
+
+// @lc code=start
+class Solution {
+    public boolean canPlaceFlowers(int[] flowerbed, int n) {
+        int count = n;
+        int i = 0;
+        while(i < flowerbed.length && count > 0){
+            if(i == 0){
+                if(flowerbed.length == 1){
+                    if(flowerbed[i] == 0){
+                        count--;
+                    }
+                    break;
+                }
+                if(flowerbed[i] == 0 && flowerbed[i+1]==0){
+                    count--;
+                    i+=2;
+                }else{
+                    i++;
+                }
+            }else if(i == flowerbed.length-1){
+                if(flowerbed[i] == 0 && flowerbed[i-1] == 0){
+                    count--;
+                }
+                i++;
+            }else if(flowerbed[i] == 0){
+                if(flowerbed[i-1] == 0 && flowerbed[i+1] == 0){
+                    count--;
+                    i+=2;
+                }else{
+                    i++;
+                }
+            }else{
+                i+=2;
+            }
+        }
+        if(count <=0){
+            return true;
+        }
+        return false;
+    }
+}
+// @lc code=end
+