js中算法求数组最大值筛选数组中大于10的数数组去重翻转数组冒泡排序 1-100的和利用函数求任意两个数的和

求数组最大值

  <script>
    var arr = [2, 6, 1, 77, 52, 25, 7];
    var max = arr[0];
    for (var i = 0; i < arr.length; i++) {
        console.log(arr[i]);
        if (arr[i] > max) {
            max = arr[i];
        }
    }
    console.log('最大值为' + max);
  </script>

筛选数组中大于10的数

<script>
    //方法1
    var arr = [2, 0, 6, 1, 77, 0, 52, 0, 25, 7];
    var newArr = [];
    var j = 0;
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] > 10) {
            newArr[j] = arr[i];
            j++;
        }
    }
    console.log(arr);
    console.log(newArr);
    //方法二
    var arr = [2, 0, 6, 1, 77, 0, 52, 0, 25, 7];
    var newArr = [];
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] > 10) {
            newArr[newArr.length] = arr[i];
        }
    }
    console.log(arr);
    console.log(newArr);
</script>

数组去重

    <script>
    //去0
    var arr = [2, 0, 6, 1, 77, 0, 52, 0, 25, 7];
    var newArr = [];
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] !== 0) {
            newArr[newArr.length] = arr[i];
        }
    }
    console.log(newArr);
    
    
    //方法二
    function unique(arr) {
        var newArr = [];
        for (var i = 0; i < arr.length; i++) {
            if (newArr.indexOf(arr[i]) === -1) {
                newArr.push(arr[i]);
            }
        }
        return newArr;
    }
    // var demo = unique(['c', 'a', 'z', 'a', 'x', 'a', 'x', 'c']);
    var demo = unique(['blue', 'green', 'blue']);
    console.log(demo);
  </script>

翻转数组

    <script>
    var arr = ['red', 'green', 'blue', 'pink', 'purple'];
    var newArr = [];
    for (var i = arr.length - 1; i >= 0; i--) {
        newArr[newArr.length] = arr[i];
    }
    console.log(newArr);
</script>

冒泡排序

   <script>
    var arr = [4, 1, 2, 3];
    for (var i = 0; i <= arr.length; i++) {
        for (var j = 0; j <= arr.length - i - 1; j++) {
            if (arr[j] < arr[j + 1]) {
                var temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
    }
    console.log(arr);

    //2.数组排序（冒泡排序）
    var arr1 = [13, 4, 77, 1, 7];
    arr1.sort(function(a, b) {
        // return a - b; //升序
        return b - a; //降序
    });
    console.log(arr1);
</script>

1-100的和

   <script>
    function getSum() {
        var sum = 0;
        for (var i = 0; i <= 100; i++) {
            sum += i;
        }
        console.log(sum);
    }
    getSum();
</script>

利用函数求任意两个数的和

           //1.利用函数求任意两个数的和
    function getSum(num1, num2) {
        console.log(num1 + num2);
    }
    getSum(1, 3);
    getSum(2, 4);
    //1.利用函数求任意两个数之间的和
    function getSums(start, end) {
        var sum = 0;
        for (var i = start; i <= end; i++) {
            sum += i;
        }
        console.log(sum);
    }
    getSums(1, 100);
    getSums(2, 4);
    //3.注意点
    //（1）多个参数之间用逗号隔开
    // (2)形参可以看作是不声明的变量
</script>

求两个数的最大值

    <script>
            function getMax(num1, num2) {
        // if (num1 > num2) {
        //     return num1;
        // } else {
        //     return num2;
        // }
        return num1>num2?num1:num2
    }
    console.log(getMax(1, 3));
    console.log(getMax(11, 3));
    console.log(getMax(3, 3));
</script>

查找字符串中某个字符出现的次数

    <script>
    //核心算法：先查找第一个o的位置 
    //然后 只要indexof 返回的结果不是-1 就继续往后查找
    //因为indexOf 只能查找到第一个，所以后面的查找，一定是当前索引加1，从而继续查找
    var str = 'oabcoefoxyozzpp';
    var index = str.indexOf('o');
    var num = 0;
    while (index !== -1) {
        console.log(index);
        num++;
        index = str.indexOf('o', index + 1);
    }
    console.log('o出现的次数是：' + num);
</script>