叠罗汉1（最长递增子序列）

最新推荐文章于 2021-09-28 21:06:27 发布

原创最新推荐文章于 2021-09-28 21:06:27 发布 · 448 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#最长递增子序列 #面试

Data Structure 专栏收录该内容

147 篇文章

订阅专栏

本文探讨了最长递增子序列问题，并通过两段Java代码示例对比展示了正确的实现方式。首先介绍了错误的代码实现及存在的问题，随后给出了优化后的正确版本。

问题：如果求一个数列的最长递增子序列？

1.下面是一段有bug的代码，输出的结果也是错的，以后作为反面教材，时常复习！

package 最长递增子序列;

public class 叠罗汉1 {

    public int getHeight(int[] men, int n) {
        // write code here
        if (n == 0) {
            return 0;
        }
        int[] dp = new int[n];
        dp[0] = 1;
        for (int i = 1; i < n; i++) {
            boolean flag = true;
            for (int j = i - 1; j >= 0; j--) {
                if (men[i] > men[j]) {
                    dp[i] = dp[j] + 1;
                    flag = false;
                    break;//不可以直接break掉，如果举个反例就是       ：4 5 6 3 8序列
                }
            }
            if(flag){
                dp[i] =1;
            }//没必要设置flag，有更加优雅的方式
        }
        int res = Integer.MIN_VALUE;
        for(int i =0;i<n;i++){
            if(dp[i] > res){
                res = dp[i];
            }
        }
        return res;
    }

    public static void main(String[] args) {
        //int[] men = {1092087,253439,1229092,2638575,2592914,1545673,2357912,1464954,1482904,2115048,1039606,3019682,2499687,2603974,235944,2029011,2594318,26817,2530237,2653234,1518368,102504,751515,1273453,252197,2328429,114699,833494,2437962,1897327,2358947,728206,1694538,1111877,2304261,1550585,2795216,1128077,2526780,2408154,1675787,1569084,542965,864374,2005718,2162685,562828,1806478,489256,643066,2684533,2308573,1242746,663914,893865,1350619,920645,706738,2053610,2975455,803894,37303,108282,78804,97230,2172571,1461268,2662562,597858,1434826,1379291,2481759,671296,489579,1997678,1361658,1793206,2500057,2428656,2228999,2758410,1766219,119904,2336578,1806119,1552636,1475687,1859500,773279,882156,286334,2887969,1579820,2178007,1736233,2042787,1545966,1657224,2524335,477841,256167,973209,2432626,564747,1915507,933567,2478598};
        int[] men = {3,2,1,4,5,0};
        int n = men.length;
        System.out.println(new 叠罗汉1().getHeight(men, n));
    }

}

2.改进版的代码

package 最长递增子序列;

public class 叠罗汉1 {

    public int getHeight(int[] men, int n) {
        // write code here
        if (n == 0) {
            return 0;
        }
        int[] dp = new int[n];
        dp[0] = 1;
        for (int i = 1; i < n; i++) {
            dp[i]=1;
            for (int j = i - 1; j >= 0; j--) {
                if (men[i] > men[j]) {
                    dp[i] = Math.max(dp[i], dp[j] + 1);
                }
            }
        }
        int res = Integer.MIN_VALUE;
        for(int i =0;i<n;i++){
            if(dp[i] > res){
                res = dp[i];
            }
        }
        return res;
    }

    public static void main(String[] args) {
        int[] men = {1092087,253439,1229092,2638575,2592914,1545673,2357912,1464954,1482904,2115048,1039606,3019682,2499687,2603974,235944,2029011,2594318,26817,2530237,2653234,1518368,102504,751515,1273453,252197,2328429,114699,833494,2437962,1897327,2358947,728206,1694538,1111877,2304261,1550585,2795216,1128077,2526780,2408154,1675787,1569084,542965,864374,2005718,2162685,562828,1806478,489256,643066,2684533,2308573,1242746,663914,893865,1350619,920645,706738,2053610,2975455,803894,37303,108282,78804,97230,2172571,1461268,2662562,597858,1434826,1379291,2481759,671296,489579,1997678,1361658,1793206,2500057,2428656,2228999,2758410,1766219,119904,2336578,1806119,1552636,1475687,1859500,773279,882156,286334,2887969,1579820,2178007,1736233,2042787,1545966,1657224,2524335,477841,256167,973209,2432626,564747,1915507,933567,2478598};
        //int[] men = {3,2,1,4,5,0};
        int n = men.length;
        System.out.println(new 叠罗汉1().getHeight(men, n));
    }

}