2020.7.17 刷题

 

35. 搜索插入位置

二分查找注意下标：

class Solution {
    public int searchInsert(int[] nums, int target) {
        int n = nums.length;
        if(n == 0) return 0;
        int start = 0, end = n-1;
        int mid = (end - start)/2 + start;
        while(end > start){
            if(nums[mid] > target){
                end = mid - 1;
            }else if(nums[mid] < target){
                start = mid + 1;
            }else return mid;
            mid = (end - start)/2 + start;
        }
        return  nums[mid] >= target ? mid : mid+1;
    }
}

785. 判断二分图

可以使用dfs和bfs，以及并查集

前两个遍历图给图上色，如果存在一个节点上了两种颜色则不是二分图

java dfs

public boolean isBipartite(int[][] graph) {
        int[] visited = new int[graph.length];

        for (int i = 0; i < graph.length; i++) {
            if(visited[i] == 0 && !dfs(graph, i, 1, visited))
                return false;
        }
        return true;
    }
    public boolean dfs(int[][]graph, int v, int color, int[]visted){
        if(visted[v] != 0){
            return visted[v] == color;
        }
        visted[v] = color;
        for (int x : graph[v]) {
            if(!dfs(graph, x, -color, visted))
                return false;
        }
        return true;
    }

bfs

public boolean isBipartite(int[][] graph) {
        int[] visited = new int[graph.length];
        Queue<Integer> queue = new LinkedList<Integer>();

        for (int i = 0; i < graph.length; i++) {
            if(visited[i] != 0){
                continue;
            }
            queue.offer(i);
            visited[i] = 1;
            while(!queue.isEmpty()){
                int v = queue.poll();
                for(int x : graph[v]){
                    if(visited[x] == visited[v]){
                        return false;
                    }
                    if (visited[x] == 0){
                        visited[x] = -visited[v];
                        queue.offer(x);
                    }
                }
            }
        }

        return true;
    }

并查集 概念